<PAGE>
 
                                                                    EXHIBIT 10.4


--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

                            WESTOWER HOLDINGS LTD.
                         WESTOWER COMMUNICATIONS LTD.


                               CREDIT AGREEMENT


                           Dated as of June 9, 1998


                            BANKBOSTON, N.A., Agent

                               -----------------

                          BANCBOSTON SECURITIES INC.,
                         Syndication Agent and Manager

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<PAGE>
 
                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                                               Page
<S>                                                                                                            <C>
1.       Definitions; Certain Rules of Construction.............................................................  1
         ------------------------------------------

2.       The Credits............................................................................................ 27
         -----------
         2.1.     Revolving Credit.............................................................................. 27
                  ----------------
                  2.1.1.   Revolving Loan....................................................................... 27
                           --------------
                  2.1.2.   Maximum Amount of Revolving Credit................................................... 27
                           ----------------------------------
                  2.1.3.   Borrowing Requests................................................................... 29
                           ------------------
                  2.1.4.   Revolving Notes...................................................................... 29
                           ---------------
                  2.1.5.   Disproportionate Advances............................................................ 30
                           -------------------------
         2.2.     Canadian Credit............................................................................... 31
                  ---------------
                  2.2.1.   Canadian Loan........................................................................ 31
                           -------------
                  2.2.2.   Maximum Amount of Canadian Credit.................................................... 31
                           ---------------------------------
                  2.2.3.   Borrowing Requests................................................................... 33
                           ------------------
                  2.2.4.   Canadian Note........................................................................ 34
                           -------------
         2.3.     Bankers' Acceptances.......................................................................... 34
                  --------------------
                  2.3.1.   Requests for Bankers' Acceptances.................................................... 34
                           ---------------------------------
                  2.3.2.   Form of Bankers' Acceptances......................................................... 34
                           ----------------------------
                  2.3.3.   Sale of Bankers' Acceptances......................................................... 35
                           ----------------------------
                  2.3.4.   Size and Maturity of Bankers' Acceptances and Rollovers.............................. 35
                           -------------------------------------------------------
                  2.3.5.   Payment of Bankers' Acceptances...................................................... 35
                           -------------------------------
                  2.3.6.   Waiver............................................................................... 36
                           ------
                  2.3.7.   Degree of Care....................................................................... 36
                           --------------
                  2.3.8.   Indemnity............................................................................ 36
                           ---------
                  2.3.9.   Obligations Absolute................................................................. 36
                           --------------------
                  2.3.10.   Depository Bills and Notes Act...................................................... 37
                            ------------------------------
                  2.3.11.   Prohibited Use of Bankers' Acceptances.............................................. 37
                            --------------------------------------
         2.4.     Letters of Credit............................................................................. 37
                  -----------------
                  2.4.1.   Issuance of Letters of Credit........................................................ 37
                           -----------------------------
                  2.4.2.   Requests for Letters of Credit....................................................... 37
                           ------------------------------
                  2.4.3.   Form and Expiration of Letters of Credit............................................. 38
                           ----------------------------------------
                  2.4.4.   Lenders' Participation in Letters of Credit.......................................... 38
                           -------------------------------------------
                  2.4.5.   Reimbursement of Payment............................................................. 38
                           ------------------------
                  2.4.6.   Uniform Customs and Practice......................................................... 38
                           ----------------------------
                  2.4.7.   Subrogation.......................................................................... 40
                           -----------
                  2.4.8.   Modification, Consent, etc........................................................... 40
                           --------------------------
         2.5.     Application of Proceeds....................................................................... 41
                  -----------------------
                  2.5.1.   Revolving Loan....................................................................... 41
                           -------------
                  2.5.2.   Canadian Loan........................................................................ 41
                           -------------
</TABLE>

                                      -i-
<PAGE>
 
<TABLE>
<CAPTION>
                                                                                                               Page
<S>                                                                                                            <C>
                  2.5.3.   Letters of Credit................................................................     41
                           -----------------                                                                     
                  2.5.4.   Specifically Prohibited Applications.............................................     41
                           ------------------------------------                                                  
         2.6.     Nature of Obligations of Lenders to Make Extensions of Credit.............................     41
                  -------------------------------------------------------------                                  
                                                                                                                 
3.       Interest; Eurodollar Pricing Options; Fees.........................................................     41
         ------------------------------------------                                                              
         3.1.     Interest..................................................................................     41
                  --------                                                                                       
         3.2.     Eurodollar Pricing Options................................................................     42
                  --------------------------                                                                     
                  3.2.1.   Election of Eurodollar Pricing Options...........................................     42
                           --------------------------------------                                                
                  3.2.2.   Notice to Lenders and Borrowers..................................................     43
                           -------------------------------                                                       
                  3.2.3.   Selection of Eurodollar Interest Periods.........................................     43
                           ----------------------------------------                                              
                  3.2.4.   Additional Interest..............................................................     44
                           -------------------                                                                   
                  3.2.5.   Violation of Legal Requirements..................................................     44
                           -------------------------------                                                       
                  3.2.6.   Funding Procedure................................................................     44
                           -----------------                                                                     
         3.3.     Commitment Fees...........................................................................     45
                  ---------------                                                                                
         3.4.     Letter of Credit Fees.....................................................................     45
                  ---------------------                                                                          
         3.5.     Changes in Circumstances; Yield Protection................................................     45
                  ------------------------------------------                                                     
                  3.5.1.   Reserve Requirements, etc........................................................     45
                           -------------------------                                                             
                  3.5.2.   Taxes............................................................................     46
                           -----                                                                                 
                  3.5.3.   Capital Adequacy.................................................................     46
                           ----------------                                                                      
                  3.5.4.   Regulatory Changes...............................................................     46
                           ------------------                                                                    
                  3.5.5.   Compensation Claims..............................................................     47
                           -------------------                                                                   
                  3.5.6.   Mitigation.......................................................................     47
                           ----------                                                                            
         3.6.     Computations of Interest and Fees.........................................................     47
                  ---------------------------------                                                              
                                                                                                                 
4.       Payment............................................................................................     48
         -------                                                                                                 
         4.1.     Payment at Maturity.......................................................................     48
                  -------------------                                                                            
         4.2.     Contingent Required Prepayments...........................................................     48
                  -------------------------------                                                                
                  4.2.1.   Excess Credit Exposure...........................................................     48
                           ----------------------                                                                
                  4.2.2.   Excess Cash Flow.................................................................     48
                           -----------------                                                                     
                  4.2.3.   Net Asset Sale Proceeds..........................................................     48
                           -----------------------                                                               
                  4.2.4.   Net Debt Proceeds................................................................     49
                           -----------------                                                                     
                  4.2.5.   Net Equity Proceeds..............................................................     49
                           -------------------                                                                   
         4.3.     Voluntary Prepayments.....................................................................     49
                  ---------------------                                                                          
         4.4.     Letters of Credit.........................................................................     49
                  -----------------                                                                              
         4.5.     Bankers' Acceptances......................................................................     50
                  --------------------                                                                           
         4.6.     Reborrowing; Application of Payments, etc.................................................     50
                  ------------------------------------------                                                     
                  4.6.1.   Reborrowing......................................................................     50
                           -----------                                                                           
                  4.6.2.   Order of Application.............................................................     50
                           --------------------                                                                  
                  4.6.3.   Payment Due......................................................................     51
                           -----------                                                                           
                  4.6.4.   Payments for Lenders.............................................................     51
                           --------------------                                                                  
         4.7.     Currency of Payments......................................................................     51
                  --------------------
</TABLE>

                                     -ii-
<PAGE>
 
<TABLE>
<CAPTION>
                                                                                                          Page
<S>                                                                                                       <C> 
5.       Conditions to Extending Credit................................................................   51
         ------------------------------                                                                    
         5.1.     Conditions on Initial Closing Date...................................................   51
                  ----------------------------------                                                       
                  5.1.1.   Notes.......................................................................   51
                           -----                                                                           
                  5.1.2.   Payment of Fees.............................................................   52
                           ---------------                                                                 
                  5.1.3.   Legal Opinions..............................................................   52
                           --------------                                                                  
                  5.1.4.   Guarantee and Security Agreement; Canadian Guarantee and Security Documents.   52
                           ---------------------------------------------------------------------------     
                  5.1.5.   Real Estate Collateral......................................................   53
                           ----------------------                                                          
                  5.1.6.   Perfection of Security......................................................   53
                           ----------------------                                                          
                  5.1.7.   Exercise of Warrants........................................................   53
                           --------------------                                                            
                  5.1.8.   Solvency, etc...............................................................   53
                           -------------                                                                   
                  5.1.9.   Adverse Market Change.......................................................   54
                           ---------------------                                                           
                  5.1.10.   Proper Proceedings.........................................................   54
                            ------------------                                                             
                  5.1.11.   General....................................................................   54
                            -------                                                                        
         5.2.     Conditions  to Each  Extension  of Credit............................................   54
                  -----------------------------------------                                                
                  5.2.1.  Officer's Certificate........................................................   54
                          ---------------------                                                            
                  5.2.2.  Legality, etc................................................................   55
                          -------------                                                                    
                                                                                                           
6.       General Covenants.............................................................................   55
         -----------------                                                                                 
         6.1.     Taxes and Other Charges; Accounts Payable............................................   55
                  -----------------------------------------                                                
                  6.1.1.   Taxes and Other Charges.....................................................   55
                           -----------------------                                                         
                  6.1.2.   Accounts Payable............................................................   55
                           ----------------                                                                
         6.2.     Conduct of Business, etc.............................................................   55
                  ------------------------                                                                 
                  6.2.1.   Types of Business...........................................................   55
                           -----------------                                                               
                  6.2.2.   Maintenance of Properties...................................................   56
                           -------------------------                                                       
                  6.2.3.   Statutory Compliance........................................................   56
                           --------------------                                                            
                  6.2.4.   Compliance with Material Agreements.........................................   56
                           -----------------------------------                                             
         6.3.     Insurance............................................................................   56
                  ---------                                                                                
                  6.3.1.   Business Interruption Insurance.............................................   56
                           -------------------------------                                                 
                  6.3.2.   Property Insurance..........................................................   56
                           ------------------                                                              
                  6.3.3.   Liability Insurance.........................................................   57
                           -------------------                                                             
                  6.3.4.   Key Executive Life Insurance................................................   57
                           ----------------------------                                                    
                  6.3.5.   Flood Insurance.............................................................   57
                           ---------------                                                                 
         6.4.     Financial Statements and Reports.....................................................   57
                  --------------------------------                                                         
                  6.4.1.   Annual Reports..............................................................   57
                           --------------                                                                  
                  6.4.2.   Quarterly Reports...........................................................   59
                           -----------------                                                               
                  6.4.3.   Currency Exchange Report; Compliance........................................   60
                           ------------------------------------                                            
                  6.4.4.   Tower Acquisition Reports...................................................   60
                           -------------------------                                                       
                  6.4.5.   Other Reports...............................................................   61
                           -------------                                                                   
                  6.4.6.   Notice of Litigation, Defaults, etc.........................................   61
                           -----------------------------------
</TABLE>

                                     -iii-
<PAGE>
 
<TABLE>
<CAPTION>
                                                                                                        Page
<S>                                                                                                     <C>
                  6.4.7.   ERISA Reports.............................................................     61
                           -------------                                                                 
                  6.4.8.   Other Information; Audit..................................................     62
                           ------------------------                                                      
         6.5.     Certain Financial Tests............................................................     62
                  -----------------------                                                                
                  6.5.1.   Consolidated Total Debt to Consolidated Adjusted EBITDA...................     62
                           -------------------------------------------------------                       
                  6.5.2.   Consolidated Senior Debt to Consolidated Adjusted EBITDA..................     63
                           --------------------------------------------------------                      
                  6.5.3.   Consolidated EBITDA to Consolidated Interest Expense......................     63
                           ----------------------------------------------------                          
                  6.5.4.   Consolidated EBITDA to Consolidated Fixed Charges.........................     63
                           -------------------------------------------------                             
                  6.5.5.   Consolidated Adjusted EBITDA..............................................     63
                           ----------------------------                                                  
                  6.5.6.   Consolidated Net Worth....................................................     64
                           ----------------------                                                        
                  6.5.7.   Capital Expenditures......................................................     64
                           --------------------                                                          
         6.6.     Indebtedness.......................................................................     64
                  ------------                                                                           
         6.7.     Guarantees; Letters of Credit......................................................     65
                  -----------------------------                                                          
         6.8.     Liens..............................................................................     66
                  -----                                                                                  
         6.9.     Investments and Acquisitions.......................................................     67
                  ----------------------------                                                           
         6.10.    Distributions......................................................................     68
                  -------------                                                                          
         6.11.    Asset Dispositions and Mergers.....................................................     68
                  ------------------------------                                                         
         6.12.    Issuance of Stock by Subsidiaries; Subsidiary Distributions........................     70
                  -----------------------------------------------------------                            
                  6.12.1.   Issuance of Stock by Subsidiaries........................................     70
                            ---------------------------------                                            
                  6.12.2.   No Restrictions on Subsidiary Distributions..............................     70
                            -------------------------------------------                                  
         6.13.    Voluntary Prepayments of Other Indebtedness........................................     70
                  -------------------------------------------                                            
         6.14.    Derivative Contracts...............................................................     70
                  --------------------                                                                   
         6.15.    Negative Pledge Clauses............................................................     70
                  -----------------------                                                                
         6.16.    ERISA, etc.........................................................................     71
                  ----------                                                                             
         6.17.    Transactions with Affiliates.......................................................     71
                  ----------------------------                                                           
         6.18.    Interest Rate Protection...........................................................     71
                  ------------------------                                                               
         6.19.    Environmental Laws.................................................................     71
                  ------------------                                                                     
                  6.19.1.   Compliance with Law and Permits..........................................     71
                            -------------------------------                                              
                  6.19.2.   Notice of Claims, etc....................................................     71
                            ---------------------                                                        
         6.20.    Tower Matters......................................................................     72
                  -------------                                                                          
                  6.20.1.   Tower Construction Requirements..........................................     72
                            -------------------------------                                              
                  6.20.2.   No Removal of Towers.....................................................     72
                            --------------------                                                         
                  6.20.3.   Pledged Towers...........................................................     72
                            --------------                                                               
                                                                                                         
7.       Representations and Warranties..............................................................     73
         ------------------------------                                                                  
         7.1.     Organization and Business..........................................................     73
                  -------------------------                                                              
                  7.1.1.   The Company...............................................................     73
                           -----------                                                                   
                  7.1.2.   Subsidiaries..............................................................     73
                           ------------                                                                  
                  7.1.3.   Qualification.............................................................     74
                           -------------                                                                 
                  7.1.4.   Capitalization............................................................     74
                           --------------                                                                
         7.2.     Financial Statements and Other Information; Material Agreements....................     74
                  ---------------------------------------------------------------                        
                  7.2.1.   Financial Statements and Other Information................................     74
                           ------------------------------------------
</TABLE>

                                     -iv-
<PAGE>
 
<TABLE>
<CAPTION>
                                                                                                        Page
<S>                                                                                                     <C>
                  7.2.2.   Material Agreements........................................................    76
                           -------------------                                                           
         7.3.     Agreements Relating to Financing Debt, Investments, etc.............................    76
                  -------------------------------------------------------                                
         7.4.     Changes in Condition................................................................    77
                  --------------------                                                                   
         7.5.     Title to Assets.....................................................................    77
                  ---------------                                                                        
         7.6.     Operations in Conformity With Law, etc..............................................    77
                  --------------------------------------                                                 
         7.7.     Litigation..........................................................................    77
                  ----------                                                                             
         7.8.     Authorization and Enforceability....................................................    77
                  --------------------------------                                                       
         7.9.     No Legal Obstacle to Agreements.....................................................    78
                  -------------------------------                                                        
         7.10.    Defaults............................................................................    78
                  --------                                                                               
         7.11.    Licenses, etc.......................................................................    78
                  -------------                                                                          
         7.12.    Tax Returns.........................................................................    79
                  -----------                                                                            
         7.13.    Certain Business Representations....................................................    79
                  --------------------------------                                                       
                  7.13.1.   Labor Relations...........................................................    79
                            ---------------                                                              
                  7.13.2.   Antitrust.................................................................    79
                            ---------                                                                    
                  7.13.3.   Real Property Leases......................................................    79
                            --------------------                                                         
                  7.13.4.   FCC, CRTC and FAA Matters.................................................    80
                            -------------------------                                                    
                  7.13.5.   Year 2000 Issues..........................................................    80
                            ----------------                                                             
                  7.13.6.   Future Expenditures.......................................................    80
                            -------------------                                                          
                  7.13.7.   Senior Subordinated Notes.................................................    80
                            -------------------------                                                    
                  7.13.8.   Payment of Fees...........................................................    80
                            ---------------                                                              
         7.14.    Environmental Regulations...........................................................    80
                  -------------------------                                                              
                  7.14.1.   Environmental Compliance..................................................    80
                            ------------------------                                                     
                  7.14.2.   Environmental Litigation..................................................    81
                            ------------------------                                                     
                  7.14.3.   Hazardous Material........................................................    81
                            ------------------                                                           
                  7.14.4.   Environmental Condition of Properties.....................................    82
                            -------------------------------------                                        
         7.15.    Pension Plans.......................................................................    82
                  -------------                                                                          
         7.16.    Government Regulation; Margin Stock.................................................    82
                  -----------------------------------                                                    
                  7.16.1.   Government Regulation.....................................................    82
                            ---------------------                                                        
                  7.16.2.   Margin Stock..............................................................    82
                            ------------                                                                 
         7.17.    Disclosure..........................................................................    82
                  ----------                                                                             
                                                                                                         
8.       Defaults.....................................................................................    83
         --------                                                                                        
         8.1.     Events of Default...................................................................    83
                  -----------------                                                                      
                  8.1.1.  Payment.....................................................................    83
                          -------                                                                        
                  8.1.2.  Specified Covenants.........................................................    83
                          -------------------                                                            
                  8.1.3.  Other Covenants.............................................................    83
                          ---------------                                                                
                  8.1.4.  Representations and Warranties..............................................    83
                          ------------------------------                                                 
                  8.1.5.  Material Financing Debt Cross Default, etc..................................    83
                          ------------------------------------------                                     
                  8.1.6.  Ownership; Liquidation; etc.................................................    84
                          ---------------------------                                                    
                  8.1.7.  Enforceability, etc.........................................................    84
                          -------------------                                                            
                  8.1.8.  Judgments...................................................................    85
                          ---------
</TABLE>

                                      -v-
<PAGE>
 
<TABLE>
<CAPTION>
                                                                                                        Page
<S>                                                                                                     <C>
                  8.1.9.  ERISA.......................................................................    85
                          -----                                                                          
                  8.1.10.  Bankruptcy, etc............................................................    85
                           ---------------                                                               
         8.2.     Certain Actions Following an Event of Default.......................................    86
                  ---------------------------------------------                                          
                  8.2.1.   Terminate Obligation to Extend Credit......................................    86
                           -------------------------------------                                         
                  8.2.2.   Specific Performance; Exercise of Rights...................................    86
                           ----------------------------------------                                      
                  8.2.3.   Acceleration...............................................................    86
                           ------------                                                                  
                  8.2.4.   Enforcement of Payment; Credit Security; Setoff............................    87
                           -----------------------------------------------                               
                  8.2.5.   Cumulative Remedies........................................................    87
                           -------------------                                                           
         8.3.     Annulment of Defaults...............................................................    87
                  ---------------------                                                                  
         8.4.     Waivers.............................................................................    87
                  -------                                                                                
                                                                                                         
9.       Expenses; Indemnity..........................................................................    88
         -------------------                                                                             
         9.1.     Expenses............................................................................    88
                  --------                                                                               
         9.2.     General Indemnity...................................................................    88
                  -----------------                                                                      
         9.3.     Indemnity with Respect to Foreign Currency Transactions.............................    89
                  -------------------------------------------------------                                
         9.4.     Indemnity With Respect to Letters of Credit.........................................    89
                  -------------------------------------------                                            
                                                                                                         
10.      Operations;  Agent...........................................................................    90
         ------------------                                                                              
         10.1.    Interests  in  Credits..............................................................    90
                  ----------------------                                                                 
         10.2.    Agent's Authority to Act, etc.......................................................    90
                  -----------------------------                                                          
         10.3.    Borrowers to Pay Agent, etc.........................................................    90
                  ---------------------------                                                            
         10.4.    Lender Operations for Advances, Letters of Credit, etc..............................    90
                  ------------------------------------------------------                                 
                  10.4.1.   Advances..................................................................    90
                            --------                                                                     
                  10.4.2.   Letters of Credit.........................................................    91
                            -----------------                                                            
                  10.4.3.   Agent to Allocate Payments, etc...........................................    91
                            -------------------------------                                              
                  10.4.4.   Delinquent Lenders; Nonperforming Lenders.................................    91
                            -----------------------------------------                                    
         10.5.    Sharing of Payments, etc............................................................    92
                  ------------------------                                                               
         10.6.    Agent's Resignation.................................................................    93
                  -------------------                                                                    
         10.7.    Concerning the Agent................................................................    93
                  --------------------                                                                   
                  10.7.1.   Action in Good Faith, etc.................................................    93
                            -------------------------                                                    
                  10.7.2.   No Implied Duties, etc....................................................    94
                            ----------------------                                                       
                  10.7.3.   Validity, etc.............................................................    94
                            -------------                                                                
                  10.7.4.   Compliance................................................................    94
                            ----------                                                                   
                  10.7.5.   Employment of Agents and Counsel..........................................    94
                            --------------------------------                                             
                  10.7.6.   Reliance on Documents and Counsel.........................................    94
                            ---------------------------------                                            
                  10.7.7.   Agent's Reimbursement.....................................................    95
                            ---------------------                                                        
         10.8.    Rights as a Lender..................................................................    95
                  ------------------                                                                     
         10.9.    Independent Credit Decision.........................................................    95
                  ---------------------------                                                            
         10.10.   Indemnification.....................................................................    96
                  ---------------                                                                        
                                                                                                         
11.      Successors and Assigns; Lender Assignments and Participations................................    96
         -------------------------------------------------------------
</TABLE>

                                     -vi-
<PAGE>
 
<TABLE>
<CAPTION>
                                                                                                        Page
<S>                                                                                                     <C>
         11.1.    Assignments by Lenders..............................................................    96
                  ----------------------                                                                 
                  11.1.1.   Assignees and Assignment Procedures.......................................    96
                            -----------------------------------                                          
                  11.1.2.   Terms of Assignment and Acceptance........................................    97
                            ----------------------------------                                           
                  11.1.3.   Register..................................................................    98
                            --------                                                                     
                  11.1.4.   Acceptance of Assignment and Assumption...................................    98
                            ---------------------------------------                                      
                  11.1.5.   Federal Reserve Bank......................................................    99
                            --------------------                                                         
                  11.1.6.   Further Assurances........................................................    99
                            ------------------                                                           
         11.2.    Credit Participants.................................................................    99
                  -------------------
         11.3.    Replacement of Lender...............................................................   100
                  ---------------------                                                                  
                                                                                                         
12.      Confidentiality..............................................................................   101
         ---------------                                                                                 
                                                                                                         
13.      Foreign Lenders..............................................................................   101
         ---------------                                                                                 
                                                                                                         
14.      Notices......................................................................................   102
         -------                                                                                         
                                                                                                         
15.      Amendments, Consents, Waivers, etc...........................................................   103
         ----------------------------------                                                              
         15.1.    Lender Consents for Amendments......................................................   103
                  ------------------------------                                                         
         15.2.    Course of Dealing; No Implied Waivers...............................................   105
                  -------------------------------------                                                  
                                                                                                         
16.      General Provisions...........................................................................   105
         ------------------                                                                              
         16.1.    Defeasance..........................................................................   105
                  ----------                                                                             
         16.2.    No Strict Construction..............................................................   105
                  ----------------------                                                                 
         16.3.    Certain Obligor Acknowledgments.....................................................   106
                  -------------------------------                                                        
         16.4.    Venue; Service of Process; Certain Waivers..........................................   106
                  ------------------------------------------                                             
         16.5.    WAIVER OF JURY TRIAL................................................................   107
                  --------------------                                                                   
         16.6.    Interpretation; Governing Law; etc..................................................   107
                  ----------------------------------
</TABLE>

                                     -vii-
<PAGE>
 
                                   EXHIBITS


2.1.4          -  Revolving Note

2.2.4          -  Canadian Note

5.1.4          -  Guarantee and Security Agreement

5.2.1          -  Officer's Certificate

6.4.           -  Compliance Certificate

6.6.8          -  Subordination Terms for Tower Debt

6.20.3A        -  Mortgage (U.S. and Canadian versions)

6.20.3B        -  Leasehold Mortgage (U.S. and Canadian versions)

6.20.3C        -  Estoppel and Consent Letter

6.20.3D        -  Local Real Estate Opinion

7.1            -  Company and its Subsidiaries

7.2.2          -  Material Agreements

7.3            -  Financing Debt, Certain Investments, etc.

7.14           -  Hazardous Material Sites

7.15           -  Multi-employer and Defined Benefit Plans

10.1           -  Percentage Interests

11.1.1         -  Assignment and Acceptance

                                    -viii-
<PAGE>
 
                            WESTOWER HOLDINGS LTD.
                         WESTOWER COMMUNICATIONS LTD.

                               CREDIT AGREEMENT


     This Agreement, dated as of June 9, 1998, is among Westower Corporation, a
Washington corporation, the Subsidiaries of Westower Corporation from time to
time party hereto, including Westower Holdings Ltd., a Wyoming corporation, and
Westower Communications Ltd., a British Columbia, Canada corporation, the
Lenders from time to time party hereto and BankBoston, N.A., both in its
capacity as a Lender and in its capacity as agent for itself and the other
Lenders.  The parties agree as follows:

     Recitals:  Pursuant to this Agreement, the Lenders are extending to the
     --------                                                               
U.S. Borrower a $75,000,000 revolving credit facility, including a $10,000,000
sub-allotment for Letters of Credit and a $10,000,000 sub-allotment for a
revolving loan and Bankers' Acceptances facility to the Canadian Borrower of
$10,000,000 in the Equivalent Amount of United States Funds to be made by the
Canadian Lender in Canadian Funds.  All the credit facilities mature on April
25, 2005. These credit facilities are guaranteed by the Company and the
Company's Subsidiaries and are secured by liens on substantially all the assets
of the Company and its Subsidiaries (including the stock of Subsidiaries and
real estate on which Towers contributing at least 85% of Consolidated Tower
Revenues are located) and a pledge of the stock of the Borrowers and of all of
the direct and indirect subsidiaries of the Company.  The proceeds of these
credit facilities may be used to acquire and construct Towers, to acquire Tower
Companies, for working capital and for general corporate purposes, as provided
herein.

1.   Definitions; Certain Rules of Construction.  Certain capitalized terms are
     ------------------------------------------                                
used in this Agreement and in the other Credit Documents with the specific
meanings defined below in this Section 1.  Except as otherwise explicitly
specified to the contrary or unless the context clearly requires otherwise, (a)
the capitalized term "Section" refers to sections of this Agreement, (b) the
capitalized term "Exhibit" refers to exhibits to this Agreement, (c) references
to a particular Section include all subsections thereof, (d) the word
"including" shall be construed as "including without limitation", (e) accounting
terms not otherwise defined herein have the meaning provided under GAAP, (f)
references to a particular statute or regulation include all rules and
regulations thereunder and any successor statute, regulation or rules, in each
case as from time to time in effect, (g) references to a particular Person
include such Person's successors and assigns to the extent not prohibited by
this Agreement and the other Credit Documents, (h) references to "Dollars" or
"$" mean United States Funds and (i) references to "C$" mean Canadian Funds.
References to "the date hereof" mean the date first set forth above.

     1.1.   "Accumulated Benefit Obligations" means the actuarial present value
             -------------------------------                                   
of the accumulated benefit obligations under any Plan, calculated in accordance
with Statement No. 87 of the Financial Accounting Standards Board.

     1.2.   "Affected Lender" is defined in Section 11.3.
             ---------------                             
<PAGE>
 
     1.3.   "Affiliate" means, with respect to the Company (or any other
             ---------                                                  
specified Person), any other Person directly or indirectly controlling,
controlled by or under direct or indirect common control with the Company (or
such specified Person), and shall include (a) any officer or director or general
partner of the Company (or such specified Person), (b) any Person of which the
Company (or such specified Person) or any Affiliate (as defined in clause (a)
above) of the Company (or such specified Person) shall, directly or indirectly,
beneficially own either (i) at least 10% of the outstanding equity securities
having the general power to vote or (ii) at least 10% of all equity interests or
(c) any Person directly or indirectly controlling the Company (or such specified
Person) through a management agreement, voting agreement or other contract.

     1.4.   "Agent" means BankBoston in its capacity as agent for the Lenders
             -----                                                           
hereunder, as well as its successors and assigns in such capacity pursuant to
Section 10.6.

     1.5.   "Agreed Currency" is defined in Section 9.3.
             ---------------                            

     1.6.   "Agreement" means this Credit Agreement as from time to time
             ---------
amended, modified and in effect.

     1.7.   "Applicable Margin" means (a) through November 30, 1998, no less
             -----------------
than 2.25% (with respect to the Eurodollar Rate and Bankers' Acceptances) and no
less than 0.750% (with respect to the Base Rate and the Canadian Prime Rate) and
(b) thereafter, the percentage in the table below set opposite the Reference
Total Leverage Ratio.

<TABLE>
<CAPTION>
                                      Base Rate/
                                  Canadian Prime Rate     Eurodollar Rate    Bankers' Acceptance
Reference Total Leverage Ratio     Applicable Margin     Applicable Margin    Applicable Margin
--------------------------------  -------------------   -------------------  -------------------
<S>                               <C>                   <C>                  <C>
Greater than 500%                         1.000%              2.500%                2.500%
 
Less than or equal to 500% but            0.750%              2.250%                2.250%
 greater than 450%
 
Less than or equal to 450% but            0.500%              2.000%                2.000%
 greater than 400%
 
Less than or equal to 400% but            0.250%              1.750%                1.750%
 greater than 350%
 
Less than or equal to 350%                0.000%              1.500%                1.500%
</TABLE>

Changes in the Applicable Margin shall occur on the third Banking Day after
annual or quarterly financial statements have been furnished to the Lenders in
accordance with Sections 6.4.1 or 6.4.2 from time to time; provided, however,
                                                           --------  ------- 
that the Applicable Margin with respect to Bankers' Acceptances issued before
the effective date of a change in the Applicable Margin will not be 

                                      -2-
<PAGE>
 
adjusted. In the event that the financial statements required to be delivered
pursuant to Section 6.4.1 or 6.4.2, as applicable, are not delivered when due,
then during the period from the third Banking Day following the date such
financial statements were due until the date upon which they are actually
delivered, the Applicable Margin shall be the maximum amount set forth in the
table above.

     1.8.    "Applicable Rate" means, at any date, the sum of:
              ---------------                                 

             (a) (i)  with respect to each portion of the Revolving Loan subject
             to a Eurodollar Pricing Option, the sum of the Applicable Margin
             (which may change during the Eurodollar Interest Period for such
             Eurodollar Pricing Option in accordance with the definition of
             "Applicable Margin") plus the Eurodollar Rate with respect to such
                                  ----
             Eurodollar Pricing Option;

             (ii)  with respect to each other portion of the Revolving Loan, the
             sum of the Applicable Margin plus the Base Rate;
                                          ----               

             (iii) with respect to each portion of the Canadian Loan (other than
             any portion of the Canadian Loan subject to Bankers' Acceptances),
             the sum of the Applicable Margin plus the Canadian Prime Rate;
                                              ----                         

     plus    (b)   an additional 2% per annum effective on the day the Agent
     ----                                                                  
             provides written notice to the Borrowers that the interest rates
             hereunder are increasing as a result of the occurrence and
             continuance of an Event of Default until the earlier of such time
             as (i) such Event of Default is no longer continuing or (ii) such
             Event of Default is deemed no longer to exist, in each case
             pursuant to Section 8.3.

     1.9.    "Assignee" is defined in Section 11.1.1.
              --------                               

     1.10.   "Assignment and Acceptance" is defined in Section 11.1.1.
              -------------------------                               

     1.11.   "Available Fund" means, at any date, an amount equal to the sum of
              --------------                                                   
(a) 50% of Consolidated Net Income calculated for the period (taken as one
accounting period) commencing on March 1, 1998 and terminating at the end of the
Company's most recently completed fiscal quarter preceding such date plus (b)
                                                                     ----    
Available Proceeds.

     1.12.   "Available Proceeds" means, at any date, an amount equal to the sum
              ------------------                                                
of (a) net cash proceeds to the Company raised after March 1, 1998 in all
underwritten public offerings or private placements of the Company's capital
stock or warrants (other than the warrant issued in connection with the Senior
Subordinated Debt) to purchase shares of capital stock (net of any brokers',
dealers', placement agents' and underwriters' fees and commissions and other
offering or placement expenses), (b) the proceeds from the exercise of options
or warrants to purchase 

                                      -3-
<PAGE>
 
capital stock and (c) the amount of Indebtedness that is converted into or
exchanged for capital stock of the Company.

     1.13.   "BA Discount Proceeds" means, in respect of any Bankers'
              --------------------
Acceptance, an amount calculated on the applicable Drawdown Date (rounded to the
nearest full cent, with one-half of one cent being rounded up) equal to the
quotient of:

             (a)  the face amount of such Bankers' Acceptance,

             divided by (b) the sum of one plus the product (rounded to the
             ------- --                    ----
             nearest multiple of 0.001%) of:

                   (i)   the BA Discount Rate applicable thereto expressed as a
             decimal multiplied by
                     -------------

                   (ii)  a fraction (A) the numerator of which is the number of
             days in the term of such Bankers' Acceptance and (B) the
             denominator of which is 365.

     1.14.   "BA Discount Rate" means, with respect to any Bankers' Acceptance
              ----------------
on any Drawdown Date, the discount rate calculated on the basis of a 365-day
year generally quoted by the Canadian Lender and determined in accordance with
normal market practice at or about 10:00 a.m. (Toronto time) for bankers'
acceptances having a comparable face amount and maturity as such Bankers'
Acceptance; provided, however, that in no event shall the foregoing rate exceed
            --------  -------
the sum of (a) 0.07% (calculated on the basis of a 365-day year) plus (b) the
                                                                 ----
average rate for Canadian Dollar bankers' acceptances accepted by the Canadian
Lender having a comparable maturity date appearing on the Reuters Screen CDOR
Page at 10:00 a.m. (Toronto time) on such Drawdown Date.

     1.15.   "BankBoston" means BankBoston, N.A.
              ----------                        

     1.16.   "Bankers' Acceptance" means drafts or bills of exchange in Canadian
              -------------------                                               
Funds drawn by the Canadian Borrower and accepted by the Canadian Lender
pursuant to this Agreement.

     1.17.   "Bankers' Acceptance Fee" means the product of (a) the product of
              -----------------------
(i) the face amount of each Bankers' Acceptance multiplied by (ii) the
Applicable Margin for Bankers' Acceptances multiplied by (b) a fraction, (i) the
                                           ----------
numerator of which is the duration of the term of such Bankers' Acceptance on
the basis of the actual number of days to elapse from and including the date of
acceptance of a Bankers' Acceptance by the Canadian Lender up to but excluding
the maturity date of the Bankers' Acceptance, and (ii) the denominator of which
is 365.

                                      -4-
<PAGE>
 
     1.18.   "Banking Day" means any day other than Saturday, Sunday or a day on
              -----------                                                       
which banks in Boston, Massachusetts or, in the case of the Canadian Loan, banks
in Toronto, Canada are authorized or required by law or other governmental
action to close and, if such term is used with reference to a Eurodollar Pricing
Option, any day on which dealings are effected in the Eurodollars in question by
first-class banks in the inter-bank Eurodollar markets in New York, New York.

     1.19.   "Bankruptcy Code" means, collectively, Title 11 of the United
              ---------------
States Code, the Bankruptcy and Insolvency Act (Canada) and the Companies'
Creditors Arrangement Act (Canada).

     1.20.   "Bankruptcy Default" means an Event of Default referred to in
              ------------------
Section 8.1.10.

     1.21.   "Base Rate" means, on any date, the greater of (a) the rate of
              ---------                                                    
interest announced by BankBoston at the Boston Office as its Base Rate or (b)
the sum of 1/2% plus the Federal Funds Rate.
                ----                        

     1.22.   "Borrowers" means each of the U.S. Borrower and the Canadian
              ---------                                                  
Borrower.

     1.23.   "Boston Office" means the principal banking office of BankBoston in
              -------------                                                     
Boston, Massachusetts.

     1.24.   "By-laws" means all written by-laws, rules, regulations and all
other documents relating to the management, governance or internal regulation of
any Person other than an individual, or interpretive of the Charter of such
Person, all as from time to time in effect.

     1.25.   "Canadian Borrower" means Westower Communications Ltd., a British
              -----------------                                               
Columbia, Canada corporation.

     1.26.   "Canadian Funds" means such coin or currency of Canada as at the
              --------------
time shall be legal tender therein for the payment of public and private debts.

     1.27.   "Canadian Guarantee and Security Documents" is defined in Section
              -----------------------------------------                       
5.1.4.

     1.28.   "Canadian Lender" means Paribas Bank of Canada, an Affiliate of
              ---------------                                               
Paribas.

     1.29.   "Canadian Loan" means, at any date, the sum of (a) the portion of
              ------------- 
the Loan advanced to the Canadian Borrower by the Canadian Lender in Canadian
Funds pursuant to Section 2.2 plus (b) the face amount of Bankers' Acceptances
issued in accordance with Section 2.3 then outstanding. The amount of the
Canadian Loan shall be calculated for purposes of the Maximum Amount of Credit
and financial covenants as the Equivalent Amount of United States Funds
determined by currency exchange rates on the date of each respective advance
until such 

                                      -5-
<PAGE>
 
advance is repaid (on a first-advanced, first-repaid method of calculation);
provided, however, that in the event that:
--------  -------                         

             (i)  the amount of the Canadian Loan determined on the foregoing
     basis is more than 5% greater or smaller than

             (ii) the amount of the Canadian Loan calculated as the Equivalent
     Amount of United States Funds determined by currency exchange rates on the
     last day of any month in accordance with Section 6.4.3(b),

the amount of the Canadian Loan shall be calculated as provided in clause (ii)
above.

     1.30.   "Canadian Note" is defined in Section 2.2.4.
              -------------                              

     1.31.   "Canadian Office" means the principal banking office of Paribas 
              ---------------     
Bank of Canada in Toronto, Canada.

     1.32.   "Canadian Prime Rate" means, on any day, the greater of:
              -------------------                                    

             (a)   the variable rate of interest expressed as a percentage per
     annum determined, announced and adjusted by the Canadian Lender on such
     date as its reference rate for commercial loans made by it in Canada in
     Canadian Funds; and

             (b)   the sum of (i) the average rate for 30-day Canadian Funds
     bankers' acceptances that appears on the Reuters Screen CDOR Page at 10:00
     a.m. (Toronto time) on such date plus (ii) 3/4% per annum.
                                      ----                     

     1.33.   "Capital Expenditures" means, for any period, amounts added or
              --------------------                                         
required to be added to the property, plant and equipment or other fixed assets
account on the Consolidated balance sheet of the Company and its Subsidiaries,
prepared in accordance with GAAP, in respect of (a) the acquisition,
construction, improvement or replacement of land, buildings, machinery,
equipment, leaseholds and any other real or personal property, (b) to the extent
not included in clause (a) above, materials, contract labor and direct labor
relating thereto (excluding amounts properly expensed as repairs and maintenance
in accordance with GAAP) and (c) software development costs to the extent not
expensed; provided, however, that Capital Expenditures shall not include (i) the
          --------  -------                                                     
purchase price for the acquisition of another Person (or substantially all the
assets of another Person) as a going concern permitted by Section 6.9, (ii)
Tower acquisition costs or (iii) prior to April 30, 2000, Tower construction
costs.

     1.34.   "Capitalized Lease" means any lease which is required to be
              -----------------                                         
capitalized on the balance sheet of the lessee in accordance with GAAP,
including Statement Nos. 13 and 98 of the Financial Accounting Standards Board.

                                      -6-
<PAGE>
 
     1.35.   "Capitalized Lease Obligations" means the amount of the liability
              -----------------------------                                   
reflecting the aggregate discounted amount of future payments under all
Capitalized Leases calculated in accordance with GAAP, including Statement Nos.
13 and 98 of the Financial Accounting Standards Board.

     1.36.   "Cash Equivalents" means:
              ----------------        

             (a)   negotiable certificates of deposit, time deposits (including
     sweep accounts), demand deposits and bankers' acceptances having a maturity
     of nine months or less and issued by any United States financial
     institution having capital and surplus and undivided profits aggregating at
     least $100,000,000 and rated at least Prime-1 by Moody's or A-1 by S&P or
     issued by any Lender;

             (b)   corporate obligations having a maturity of nine months or
     less and rated at least Prime-1 by Moody's or A-1 by S&P or issued by any
     Lender;

             (c)   any direct obligation of the United States of America or any
     agency or instrumentality thereof, or of any state or municipality thereof,
     (i) which has a remaining maturity at the time of purchase of not more than
     one year or which is subject to a repurchase agreement with any Lender (or
     any other financial institution referred to in clause (a) above)
     exercisable within one year from the time of purchase and (ii) which, in
     the case of obligations of any state or municipality, is rated at least Aaa
     by Moody's or AAA by S&P;

             (d)   any mutual fund or other pooled investment vehicle rated at
     least Aa by Moody's or AA by S&P which invests principally in obligations
     described above; and

             (e)   any Investment by a Foreign Subsidiary in its local
     jurisdiction comparable to the items described above.

     1.37.   "CERCLA" means the federal Comprehensive Environmental Response,
              ------                                                         
Compensation and Liability Act of 1980 and any similar statute under Canadian
law.

     1.38.   "Charter" means the articles of organization, certificate of
              -------                                                    
incorporation, statute, constitution, joint venture agreement, partnership
agreement, trust indenture, limited liability company agreement or other charter
document of any Person other than an individual, each as from time to time in
effect.

     1.39.   "Closing Date" means the Initial Closing Date and each other date 
              ------------                          
on which any extension of credit is made pursuant to Sections 2.1, 2.2, 2.3 or
2.4.

     1.40.   "Code" means the federal Internal Revenue Code of 1986 and any
              ----                                                         
similar statute under Canadian law.

                                      -7-
<PAGE>
 
     1.41.   "Commitment" means, with respect to any Lender, such Lender's
              ----------                                                  
obligations to extend the respective credits contemplated by Section 2 and its
interests in such credits at any time outstanding.  The original Commitments are
set forth in Exhibit 10.1 and the subsequent Commitments are recorded from time
to time in the Register.

     1.42.   "Commitment Fee Rate" means, with respect to any Payment Date, (a)
              -------------------                                              
through November 30, 1998, 0.500%, (b) 0.500% in the event that the Reference
Total Leverage Ratio exceeds 400%, (c) 0.375% in the event that the Reference
Total Leverage Ratio exceeds 350%, but is less than or equal to 400%, and (d)
0.300% in all other events.

     1.43.   "Communications Act" means the federal Communications Act of 1934 
              ------------------             
and any similar statute under Canadian law.

     1.44.   "Company" means Westower Corporation, a Washington corporation.
              -------                                                       

     1.45.   "Computation Covenants" means Sections 6.5, 6.6.7, 6.6.8, 6.6.14,
              ---------------------                                           
6.9.5, 6.10.3, 6.11.2, 6.11.6, 6.11.7 and 6.16 and the definition of "Tower Cash
Flow Availability."

     1.46.   "Consolidated" and "Consolidating", when used with reference to any
              ------------       -------------                                  
term, mean that term as applied to the accounts of the Company (or other
specified Person) and all of its Subsidiaries (or other specified group of
Persons), or such of its Subsidiaries as may be specified, consolidated (or
combined) or consolidating (or combining), as the case may be, in accordance
with GAAP and with appropriate deductions for minority interests in
Subsidiaries.

     1.47.   "Consolidated Adjusted EBITDA" means, for any period, the total of
              ----------------------------                                     
Consolidated EBITDA minus Consolidated Tower Cash Flow plus Consolidated
                    -----                              ----             
Annualized Tower Cash Flow.

     1.48.   "Consolidated Annualized Tower Cash Flow" means, for any fiscal
              ---------------------------------------                       
quarter, the product of (a) Consolidated Tower Cash Flow multiplied by (b) four.

     1.49.   "Consolidated EBITDA" means, for any period, the total of:
              -------------------                                      

             (a)   Consolidated Net Income;

     plus    (b)   all amounts deducted in computing such Consolidated Net
     ----                                                                      
                   Income in respect of:

                   (i)  depreciation, amortization and other noncash charges
             (including deferred taxes and excluding reserves),
 
                   (ii) Consolidated Interest Expense, and
 

                                      -8-
<PAGE>
 
                   (iii) taxes based upon or measured by net income that are
             actually paid in cash during such period,
            
     minus   (c)   all amounts included in Consolidated Net Income in respect 
     -----
                   of deferred income tax benefits.
 
     1.50.   "Consolidated Excess Cash Flow" means, for any period, the total
              ----------------------------- 
     of:

             (a)   Consolidated EBITDA,
 
     minus   (b)   Capital Expenditures,
     -----
 
     minus   (c)   taxes based upon or measured by net income that are actually
     -----
     paid in cash,

     minus   (d)   Consolidated Fixed Charges (but in no event including 
     -----    
     contingent prepayments required by Section 4.3),

     minus   (e)   voluntary prepayments of term Financing Debt of the Company 
     -----
     and its Subsidiaries permitted by this Agreement.            
 
     1.51.   "Consolidated Fixed Charges" means, for any period, the sum of:
              --------------------------                                    

             (a)   Consolidated Interest Expense,

     plus    (b)   the aggregate amount of all mandatory scheduled payments,
     ----                                                                
     mandatory scheduled prepayments, sinking fund payments and mandatory
     reductions in revolving loans as a result of mandatory reductions in
     revolving credit availability, all with respect to Financing Debt of the
     Company and its Subsidiaries in accordance with GAAP on a Consolidated
     basis, including payments in the nature of principal under Capitalized
     Leases and Bankers' Acceptances, but in no event including contingent
     prepayments required by Section 4.3,

     plus    (c)   any mandatory dividends paid or payable in cash by the 
     ----                                                                     
     Company or any of its Subsidiaries to third parties,

     plus    (d)   Capital Expenditures,
     ----                            

     plus    (e)   taxes based upon or measured by net income that are actually
     ----                                                                   
     paid in cash during such period.

     1.52.   "Consolidated Interest Expense" means, for any period, the total 
              -----------------------------        
of:

                                      -9-
<PAGE>
 
             (a)   the aggregate amount of interest, including commitment fees,
     payments in the nature of interest under Capitalized Leases, Bankers'
     Acceptance Fees, discounts on Bankers' Acceptances and net payments under
     Interest Rate Protection Agreements, accrued by the Company and its
     Subsidiaries (whether such interest is reflected as an item of expense or
     capitalized) in accordance in accordance with GAAP on a Consolidated basis,

     minus   (b)   to the extent otherwise included in clause (a) above, the
     -----                                                               
     amortization of deferred financing fees and costs, original issue discount
     relating to Indebtedness and accrued interest on Indebtedness not paid in
     cash to the extent permitted by the terms, including subordination terms,
     of such Indebtedness (including PIK Interest),

     plus    (c)   actual cash payments with respect to accrued and unpaid 
     ----                                                                       
     interest (including PIK Interest) that has previously reduced Consolidated
     Interest Expense pursuant to clause (b) above.

     1.53.   "Consolidated Net Income" means, for any period, the net income (or
              -----------------------                                           
loss) of the Company and its Subsidiaries, determined in accordance with GAAP on
a Consolidated basis; provided, however, that in the event during such period
                      --------  -------                                      
the Company and its Subsidiaries make an acquisition permitted by Section 6.9
(whether through stock purchase, asset purchase, merger or consolidation),
Consolidated Net Income shall include the income (or loss) of such acquired
Person (or acquired assets) accrued during such period prior to the date of such
acquisition; and provided, further, however, that Consolidated Net Income shall
                 --------  -------  -------                                    
not include:

             (a)   except as provided in the preceding proviso, the income (or
     loss) of any Person (other than a Subsidiary) in which the Company or any
     of its Subsidiaries has an ownership interest; provided, however, that (i)
                                                    --------  -------          
     Consolidated Net Income shall include amounts in respect of the income of
     such Person when actually received in cash by the Company or such
     Subsidiary in the form of dividends or similar Distributions and (ii)
     Consolidated Net Income shall be reduced by the aggregate amount of all
     Investments, regardless of the form thereof, made by the Company or any of
     its Subsidiaries in such Person for the purpose of funding any deficit or
     loss of such Person;

             (b)   all amounts included in computing such net income (or loss)
     in respect of the retirement of any Indebtedness or equity at less than
     face value after February 28, 1998;

             (c)   extraordinary and nonrecurring gains;

             (d)   the income of any Subsidiary to the extent the payment of
     such income in the form of a Distribution or repayment of Indebtedness to
     the Company or a Wholly Owned Subsidiary is not permitted, whether on
     account of any Charter or By-law

                                      -10-
<PAGE>
 
     restriction, any agreement, instrument, deed or lease or any law, statute,
     judgment, decree or governmental order, rule or regulation applicable to
     such Subsidiary; and
     
             (e)   any after-tax gains or losses attributable to returned
     surplus assets of any Plan.

     1.54.   "Consolidated Net Worth" means, at any date, (a) all amounts in
              ----------------------                                        
respect of the Company's capital stock, plus the amounts of additional paid-in
capital, retained earnings and other items designated as part of the Company's
stockholders' equity (without including treasury stock of the Company and any
preferred stock of the Company which is referred to in clause (e) of the
definition of "Indebtedness"), all of which would appear as such on a
Consolidated balance sheet of the Company and its Subsidiaries as of such date
prepared in accordance with GAAP.

     1.55.   "Consolidated Senior Debt" means, at any date, the excess of (a)
              ------------------------                                       
Consolidated Total Debt over (b) the outstanding principal amount of the Senior
Subordinated Notes.

     1.56.   "Consolidated Total Debt" means, at any date, all Financing Debt of
              -----------------------                                           
the Company and its Subsidiaries on a Consolidated basis.

     1.57.   "Consolidated Tower Cash Flow" means, for any period, the remainder
              ----------------------------                                      
of (a) Consolidated Tower Revenues minus (b) the cash costs of revenues earned
                                   -----                                      
and cash selling, general and administrative expenses (but not Capital
Expenditures) associated with the maintenance and operation of Towers.

     1.58.   "Consolidated Tower Revenues" means, for any period:
              ---------------------------                        

             (a)   the net operating revenues (after reductions for discounts,
     commissions and bad debt reserves) of the Company and its Subsidiaries
     determined in accordance with GAAP on a Consolidated basis, generated from
     existing, acquired or constructed Towers, minus
                                               -----

             (b)   any proceeds included in such net operating revenues from the
     sale, refinancing, condemnation or destruction of any Tower assets.

     1.59.   "Credit Documents" means:
              ----------------        

             (a)   this Agreement, the Notes, each Letter of Credit, each draft
     presented or accepted under a Letter of Credit, Bankers' Acceptances,
     drafts or bills of exchange to be accepted as Bankers' Acceptances, the
     Guarantee and Security Agreement, the Canadian Guarantee and Security
     Documents, the fee agreement contemplated by Section 5.1.2 and each
     Interest Rate Protection Agreement provided by a Lender (or an Affiliate of
     a Lender) to the Company or any of its Subsidiaries, each as from time to
     time in effect; and

                                      -11-
<PAGE>
 
             (b)   any other present or future agreement or instrument from time
     to time entered into among the Company, any of its Subsidiaries or any
     other Obligor, on one hand, and the Agent, any Letter of Credit Issuer, the
     Canadian Lender or all the Lenders, on the other hand, relating to,
     amending or modifying this Agreement or any other Credit Document referred
     to above or which is stated to be a Credit Document, each as from time to
     time in effect.

     1.60.   "Credit Exposure" means at any date, collectively, the Revolving
              ---------------                                                
Loan, the Canadian Loan and Letter of Credit Exposure then outstanding.

     1.61.   "Credit Obligations" means all present and future liabilities,
              ------------------                                           
obligations and Indebtedness of the Company, any of its Subsidiaries or any
other Obligor owing to the Agent or any Lender (or any Affiliate of a Lender)
under or in connection with this Agreement or any other Credit Document,
including obligations in respect of principal, interest, Bankers' Acceptances,
reimbursement obligations under Letters of Credit and Interest Rate Protection
Agreements provided by a Lender (or an Affiliate of a Lender), commitment fees,
Letter of Credit fees, amounts provided for in Sections 3.2.4, 3.5 and 9 and
other fees, charges, indemnities and expenses from time to time owing hereunder
or under any other Credit Document (all whether accruing before or after a
Bankruptcy Default and regardless of whether allowed as a claim in bankruptcy or
similar proceedings).

     1.62.   "Credit Participant" is defined in Section 11.2.
              ------------------                             

     1.63.   "Credit Security" means all assets now or from time to time
              ---------------
hereafter subjected to a security interest, mortgage or charge (or intended or
required so to be subjected pursuant to the Guarantee and Security Agreement,
the Canadian Guarantee and Security Documents or any other Credit Document) to
secure the payment or performance of any of the Credit Obligations on a pari
passu basis, including the assets described in section 3.1 of the Guarantee and
Security Agreement.

     1.64.   "CRTC" means the Canadian Radio-television and Telecommunications
              ----                                                            
Commission.

     1.65.   "Default" means any Event of Default and any event or condition
              -------
which with the passage of time or giving of notice, or both, would become an
Event of Default, including the filing against the Company, any of its
Subsidiaries or any other Obligor of a petition commencing an involuntary case
under the Bankruptcy Code.

     1.66.   "Delinquency Period" is defined in Section 10.4.4.
              ------------------                               

     1.67.   "Delinquent Lender" is defined in Section 10.4.4.
              -----------------                               

                                      -12-
<PAGE>
 
     1.68.   "Delinquent Payment" is defined in Section 10.4.4.
              ------------------                               

     1.69.   "Disproportionate Advance" is defined in Section 2.1.5.
              ------------------------                              

     1.70.   "Distribution" means, with respect to the Company (or other
              ------------
specified Person):

             (a)   the declaration or payment of any dividend or distribution on
     or in respect of any shares of any class of capital stock of or other
     equity interests in the Company (or such specified Person);

             (b)   the purchase, redemption or other retirement of any shares of
     any class of capital stock of or other equity interest in the Company (or
     such specified Person) or of options, warrants or other rights for the
     purchase of such shares, directly, indirectly through a Subsidiary or
     otherwise;

             (c)   any other distribution on or in respect of any shares of any
     class of capital stock of or equity or other beneficial interest in the
     Company (or such specified Person);

             (d)   any payment of principal or interest with respect to, or any
     purchase, redemption or defeasance of, any Financing Debt of the Company
     (or such specified Person) which by its terms or the terms of any agreement
     is subordinated to the payment of the Credit Obligations; and

             (e)   any payment, loan or advance by the Company (or such
     specified Person) to, or any other Investment by the Company (or such
     specified Person) in, the holder of any shares of any class of capital
     stock of or equity interest in the Company (or such specified Person), or
     any Affiliate of such holder (including the payment of management and
     transaction fees and expenses);

provided, however, that the term "Distribution" shall not include (i) dividends
--------  -------                                                              
payable in perpetual common stock of or other similar equity interests in the
Company (or such specified Person) or (ii) payments in the ordinary course of
business in respect of (A) reasonable compensation paid to employees, officers
and directors, (B) advances and reimbursements to employees for travel expenses,
drawing accounts, relocation costs and similar expenditures, or (C) rent paid
to, or accounts payable for services rendered or goods sold by, non-Affiliates
that own capital stock of or other equity interests in the Company (or such
specified Person).

     1.71.   "Domestic Subsidiary" means any Subsidiary that is not a Foreign
              -------------------                                            
Subsidiary.

     1.72.   "Drawdown Date" means the date on which Bankers' Acceptances are
              -------------                                                  
created and purchased (or completed drafts are purchased with respect to
Bankers' Acceptances) by the Canadian Lender under Section 2.3.

                                      -13-
<PAGE>
 
     1.73.   "Environmental Laws" means all applicable federal, provincial,
              ------------------
state or local statutes, laws, ordinances, codes, rules, regulations and
guidelines (including consent decrees and administrative orders) relating to
public health and safety and protection of the environment, including the
federal Occupational Health and Safety Act.

     1.74.   "Equivalent Amount of United States Funds" means, as of any date,
              ----------------------------------------                        
with respect to a particular amount of Canadian Funds outstanding or to be
borrowed or paid at a particular place, an amount of United States Funds which
will enable the Canadian Lender to purchase such amount of Canadian Funds,
computed at the Canadian Lender's spot rate on such date at the place in
question; provided, however, that if no rate of exchange exists for effecting
          --------  -------                                                  
such spot purchases, the Equivalent Amount of United States Funds shall mean the
amount of United States Funds equivalent to the actual cost to the Canadian
Lender of obtaining the Canadian Funds in the amount and at the place in
question on such date.  For purposes of determining the amount of the Canadian
Loan at any date, the applicable Equivalent Amount of United States Funds will
be determined as follows:

      (a)  for purposes of determining the Maximum Amount of Canadian Credit
with respect to availability for an advance of the Canadian Loan, the Equivalent
Amount of United States Funds as of the proposed Closing Date for such advance
shall be used.

     (b)  for all other purposes, the Equivalent Amount of United States Funds
as of the end of the most recent month for which a currency exchange report is
then required to be furnished by Section 6.4.3.

     1.75.   "ERISA" means the federal Employee Retirement Income Security Act
              -----
of 1974 and any similar statute under Canadian law.

     1.76.   "ERISA Group Person" means the Company, any of its Subsidiaries and
              ------------------                                                
any Person which is a member of the controlled group or under common control
with the Company or any of its Subsidiaries within the meaning of section 414 of
the Code or section 4001(a)(14) of ERISA.

     1.77.   "Estoppel and Consent Letters" is defined in Section 6.20.3.
              ----------------------------                               

     1.78.   "Eurodollars" means, with respect to any Lender, deposits of United
              -----------                                                       
States Funds in a non-United States office or an international banking facility
of such Lender.

     1.79.   "Eurodollar Basic Rate" means, for any Eurodollar Interest Period,
              ---------------------                                            
the rate of interest at which Eurodollar deposits which have a term
corresponding to such Eurodollar Interest Period are offered to the Agent by
first class banks in the inter-bank Eurodollar market for delivery in
immediately available funds at a Eurodollar Office on the first day of such
Eurodollar Interest Period as determined by the Agent at approximately 10:00
a.m. (Boston time) 

                                      -14-
<PAGE>
 
two Banking Days prior to the date upon which such Eurodollar Interest Period is
to commence (which determination by the Agent shall, in the absence of manifest
error, be conclusive).

     1.80.   "Eurodollar Interest Period" means any period, selected as provided
              --------------------------                                        
in Section 3.2.1, of one, two, three or six months, commencing on any Banking
Day and ending on the corresponding date in the subsequent calendar month so
indicated (or, if such subsequent calendar month has no corresponding date, on
the last day of such subsequent calendar month); provided, however, that subject
                                                 --------  -------              
to Section 3.2.3, if any Eurodollar Interest Period so selected would otherwise
begin or end on a date which is not a Banking Day, such Eurodollar Interest
Period shall instead begin or end, as the case may be, on the immediately
preceding or succeeding Banking Day as determined by the Agent in accordance
with the then current banking practice in the inter-bank Eurodollar market with
respect to Eurodollar deposits at the applicable Eurodollar Office, which
determination by the Agent shall, in the absence of manifest error, be
conclusive.

     1.81.   "Eurodollar Office" means such non-United States office or
              -----------------                                        
international banking facility of any Lender as such Lender may from time to
time select.

     1.82.   "Eurodollar Pricing Options" means the options granted pursuant to
              --------------------------                                       
Section 3.2.1 to have the interest on any portion of the Loan computed on the
basis of a Eurodollar Rate.

     1.83.   "Eurodollar Rate" for any Eurodollar Interest Period means the
              ---------------
rate, rounded upward to the nearest 1/100%, obtained by dividing (a) the
Eurodollar Basic Rate for such Eurodollar Interest Period by (b) an amount equal
to 1 minus the Eurodollar Reserve Rate; provided, however, that if at any time
     -----                              --------  -------
during such Eurodollar Interest Period the Eurodollar Reserve Rate applicable to
any outstanding Eurodollar Pricing Option changes, the Eurodollar Rate for such
Eurodollar Interest Period shall automatically be adjusted to reflect such
change, effective as of the date of such change to the extent required by the
Legal Requirement implementing such change.

     1.84.   "Eurodollar Reserve Rate" means the stated maximum rate (expressed
              -----------------------
as a decimal) of all reserves (including any basic, supplemental, marginal or
emergency reserve or any reserve asset), if any, as from time to time in effect,
required by any Legal Requirement to be maintained by any Lender against (a)
"Eurocurrency liabilities" as specified in Regulation D of the Board of
Governors of the Federal Reserve System applicable to Eurodollar Pricing
Options, (b) any other category of liabilities that includes Eurodollar deposits
by reference to which the interest rate on portions of the Loan subject to
Eurodollar Pricing Options is determined, (c) the principal amount of or
interest on any portion of the Loan subject to a Eurodollar Pricing Option or
(d) any other category of extensions of credit, or other assets, that includes
loans subject to a Eurodollar Pricing Option by a non-United States office of
any of the Lenders to United States residents, in each case without the benefits
of credits for prorations, exceptions or offsets that may be available to a
Lender.

                                      -15-
<PAGE>
 
     1.85.   "Event of Default" is defined in Section 8.1.
              ----------------                            

     1.86.   "Exchange Act" means the federal Securities Exchange Act of 1934.
              ------------                                                    

     1.87.   "FAA" means the Federal Aviation Administration.
              ---                                            

     1.88.   "FCC" means the Federal Communications Commission.
              ---                                              

     1.89.   "Federal Funds Rate" means, for any day, the rate equal to the
              ------------------                                           
weighted average (rounded upward to the nearest 1/16%) of (a) the rates on
overnight federal funds transactions with members of the Federal Reserve System
arranged by federal funds brokers, as such weighted average is published for
such day (or, if such day is not a Banking Day, for the immediately preceding
Banking Day) by the Federal Reserve Bank of New York or (b) if such rate is not
so published for such Banking Day, quotations received by the Agent from three
federal funds brokers of recognized standing selected by the Agent.  Each
determination by the Agent of the Federal Funds Rate shall, in the absence of
manifest error, be conclusive.

     1.90.   "Final Maturity Date" means April 25, 2005.
              -------------------                       

     1.91.   "Financial Officer" of the Company (or other specified Person)
              -----------------
means its chief executive officer, chief financial officer, chief operating
officer, chairman, president, treasurer, controller or any of its vice
presidents whose primary responsibility is for its financial affairs, in each
case whose incumbency and signatures have been certified to the Agent by the
secretary or other appropriate attesting officer of the Company (or such
specified Person).

     1.92.   "Financing Debt" means each of the items described in clauses (a)
              --------------                                                  
through (f) of the definition of the term "Indebtedness" and, without
duplication, any Guarantees of such items.

     1.93.   "Foreign Subsidiary" means each Subsidiary that is organized under
              ------------------                                               
the laws of, and conducting its business primarily in a jurisdiction outside of,
the United States of America and that is not domesticated or dually incorporated
under the laws of the United States of America or the states thereof.

     1.94.   "Funding Liability" means (a) any Eurodollar deposit which was used
              -----------------                                                 
(or deemed by Section 3.2.6 to have been used) to fund any portion of the Loan
subject to a Eurodollar Pricing Option, and (b) any portion of the Loan subject
to a Eurodollar Pricing Option funded (or deemed by Section 3.2.6 to have been
funded) with the proceeds of any such Eurodollar deposit.

     1.95.   "GAAP" means generally accepted accounting principles as from time
              ----
to time in effect, including the statements and interpretations of the United
States Financial Accounting Standards Board; provided, however, that (a) for
                                             --------  -------
purposes of compliance with Sections 4.2.2, 6

                                      -16-
<PAGE>
 
(other than Section 6.4) and the related definitions, "GAAP" means such
principles as in effect on February 28, 1998 as applied by the Company and its
Subsidiaries in the preparation of the most recent annual statements referred to
in Section 7.2.1(a), and consistently followed, without giving effect to any
subsequent changes thereto and (b) in the event of a change in generally
accepted accounting principles after such date, either the Company or the
Required Lenders may request a change in the definition of "GAAP", in which case
the parties hereto shall negotiate in good faith with respect to an amendment of
this Agreement implementing such change.

     1.96.   "Guarantee" means, with respect to the Company (or other specified
              ---------                                                        
Person):

             (a)   any guarantee by the Company (or such specified Person) of
     the payment or performance of, or any contingent obligation by the Company
     (or such specified Person) in respect of, any Indebtedness or other
     obligation of any primary obligor;

             (b)   any other arrangement whereby credit is extended to a primary
     obligor on the basis of any promise or undertaking of the Company (or such
     specified Person), including any binding "comfort letter" or "keep well
     agreement" written by the Company (or such specified Person), to a creditor
     or prospective creditor of such primary obligor, to (i) pay the
     Indebtedness of such primary obligor, (ii) purchase an obligation owed by
     such primary obligor, (iii) pay for the purchase or lease of assets or
     services regardless of the actual delivery thereof or (iv) maintain the
     capital, working capital, solvency or general financial condition of such
     primary obligor;

             (c)   any liability of the Company (or such specified Person), as a
     general partner of a partnership in respect of Indebtedness or other
     obligations of such partnership;

             (d)   any liability of the Company (or such specified Person) as a
     joint venturer of a joint venture in respect of Indebtedness or other
     obligations of such joint venture;

             (e)   any liability of the Company (or such specified Person) with
     respect to the tax liability of others as a member of a group (other than a
     group consisting solely of the Company and its Subsidiaries) that is
     consolidated for tax purposes; and

             (f)   reimbursement obligations, whether contingent or matured, of
     the Company (or such specified Person) with respect to letters of credit,
     bankers acceptances, surety bonds, other financial guarantees and Interest
     Rate Protection Agreements,

in each case whether or not any of the foregoing are reflected on the balance
sheet of the Company (or such specified Person) or in a footnote thereto;
provided, however, that the term "Guarantee" shall not include endorsements for
--------  -------                                                              
collection or deposit in the ordinary course of business.  The amount of any
Guarantee and the amount of Indebtedness resulting from such Guarantee shall be
the maximum amount that the guarantor may become obligated to pay in 

                                      -17-
<PAGE>
 
respect of the obligations (whether or not such obligations are outstanding at
the time of computation).

     1.97.    "Guarantee and Security Agreement" is defined in Section 5.1.4.
               --------------------------------                              

     1.98.    "Guarantor" means the Company and each of its Subsidiaries party
               ---------
to, or which subsequently becomes party to, the Guarantee and Security Agreement
or the Canadian Guarantee and Security Documents as a Guarantor.

     1.99.    "Hazardous Material" means any pollutant, toxic or hazardous
               ------------------
material or waste, including any "hazardous substance" or "pollutant" or
"contaminant" as defined in section 101(14) of CERCLA or any other Environmental
Law or regulated as toxic or hazardous under RCRA or any other Environmental
Law.

     1.100.   "Indebtedness" means all obligations, contingent or otherwise,
               ------------
which in accordance with GAAP are required to be classified upon the balance
sheet of the Company (or other specified Person) as liabilities, but in any
event including (without duplication):

              (a)   borrowed money;

              (b)   indebtedness evidenced by notes, debentures or similar
     instruments;

              (c)   Capitalized Lease Obligations;

              (d)   the deferred purchase price of assets, services or
     securities, including related noncompetition, consulting and stock
     repurchase obligations (other than ordinary trade accounts payable within
     six months after the incurrence thereof in the ordinary course of
     business);

              (e)   mandatory redemption or dividend rights on capital stock (or
     other equity);

              (f)   reimbursement obligations, whether contingent or matured,
     with respect to letters of credit, Bankers' Acceptances and similar
     instruments, surety bonds, other financial guarantees and Interest Rate
     Protection Agreements (without duplication of other Indebtedness supported
     or guaranteed thereby);

              (g)   unfunded pension liabilities;

              (h)   obligations that are immediately and directly due and
     payable out of the proceeds of or production from property;

                                      -18-
<PAGE>
 
              (i)   liabilities secured by any Lien existing on property owned
     or acquired by the Company (or such specified Person), whether or not the
     liability secured thereby shall have been assumed; and

              (j)   all Guarantees in respect of Indebtedness of others.

     1.101.   "Indemnified Party" is defined in Section 9.2.
               -----------------                            

     1.102.   "Initial Closing Date" means such date agreed to by the Company
               --------------------
and the Agent as the Closing Date for the first extension of credit hereunder.

     1.103.   "Interest Rate Protection Agreement" means any interest rate swap,
               ----------------------------------                               
interest rate cap, interest rate hedge or other contractual arrangement that
converts variable interest rates into fixed interest rates, fixed interest rates
into variable interest rates or other similar arrangements.

     1.104.   "Investment" means, with respect to the Company (or other
               ----------
specified Person):

              (a)   any share of capital stock, partnership or other equity
     interest, evidence of Indebtedness or other security issued by any other
     Person;

              (b)   any loan, advance or extension of credit to, or contribution
     to the capital of, any other Person;

              (c)   any Guarantee of the obligations of any other Person;

              (d)   any acquisition of all, or any division or similar operating
     unit of, the business of any other Person or the assets comprising such
     business, division or unit; and

              (e)   any other similar investment.

     The investments described in the foregoing clauses (a) through (e) shall be
included in the term "Investment" whether they are made or acquired by purchase,
exchange, issuance of stock or other securities, merger, reorganization or any
other method; provided, however, that the term "Investment" shall not include
              --------  -------                                              
(i) trade and customer accounts receivable for property leased, goods furnished
or services rendered in the ordinary course of business and payable within one
year in accordance with customary trade terms, (ii) deposits, advances or
prepayments to suppliers for property leased or licensed, goods furnished and
services rendered in the ordinary course of business, (iii) advances to
employees for relocation and travel expenses, drawing accounts and similar
expenditures, (iv) stock or other securities acquired in connection with the
satisfaction or enforcement of Indebtedness or claims due to the Company (or
such specified Person) or as security for any such Indebtedness or claim or (v)
demand deposits in banks or similar financial institutions.

                                      -19-
<PAGE>
 
     In determining the amount of outstanding Investments:

              (A)  the amount of any Investment shall be the cost thereof minus
                                                                          -----
      any returns of capital in cash on such Investment (determined in
      accordance with GAAP without regard to amounts realized as income on such
      Investment);

              (B)  the amount of any Investment in respect of a purchase
     described in clause (d) above shall include the amount of any Financing
     Debt assumed in connection with such purchase or secured by any asset
     acquired in such purchase (whether or not any Financing Debt is assumed) or
     for which any Person that becomes a Subsidiary is liable on the date on
     which the securities of such Person are acquired; and

              (C)  no Investment shall be increased as the result of an increase
     in the undistributed retained earnings of the Person in which the
     Investment was made or decreased as a result of an equity interest in the
     losses of such Person.

     1.105.   "Leases" means the leases with respect to real property on which
               ------                                                         
Towers are located.

     1.106.   "Legal Requirement" means any present or future requirement
               -----------------
imposed upon any of the Lenders or the Company and its Subsidiaries by any law,
statute, rule, regulation, directive, order, decree or guideline (or any
interpretation thereof by courts or of administrative bodies) of the United
States of America or Canada, or any jurisdiction in which any Eurodollar Office
is located or any state or political subdivision of any of the foregoing, or by
any board, governmental or administrative agency, central bank or monetary
authority of the United States of America or Canada, any jurisdiction in which
any Eurodollar Office is located or where the Company or any of its Subsidiaries
owns property or conducts its business, or any political subdivision of any of
the foregoing. Any such law, statute, rule, regulation, directive, order,
decree, guideline or interpretation imposed on any of the Lenders not having the
force of law shall be deemed to be a Legal Requirement for purposes of Section 3
if such Lender reasonably believes that compliance therewith is customary
commercial practice.

     1.107.   "Lender" means each of the Persons listed as lenders on the
               ------
signature page hereto, including BankBoston in its capacity as a Lender and such
other Persons who may from time to time own a Percentage Interest in the Credit
Obligations, but the term "Lender" shall not include any Credit Participant.

     1.108.   "Lending Officer" means such individuals whom the Agent (or the
               ---------------                                               
Canadian Lender, as the case may be) may designate by notice to the Borrowers
from time to time as an officer or employee who may receive telephone requests
for extensions of credit under Sections 2.1.3 and 2.4.2 (or Sections 2.2.3 or
2.3.1, as the case may be).

     1.109.   "Letter of Credit" is defined in Section 2.4.1.
               ----------------                              

                                      -20-
<PAGE>
 
     1.110.    "Letter of Credit Exposure" means, at any date, the sum of (a)
                -------------------------
the aggregate face amount of all drafts that may then or thereafter be presented
by beneficiaries under all Letters of Credit then outstanding, plus (b) the
aggregate face amount of all drafts that the Letter of Credit Issuer has
previously accepted under Letters of Credit but has not paid.

     1.111.    "Letter of Credit Issuer" means, for any Letter of Credit,
                -----------------------
BankBoston or, in the event BankBoston does not for any reason issue a requested
Letter of Credit, another Lender selected by the U.S. Borrower to issue such
Letter of Credit.

     1.112.    "License Agreements" means any license or lease agreements
                ------------------
between the Company or one of its Subsidiaries, on one hand, and its customers,
on the other hand, for the licensing or leasing of space on any Tower.

     1.113.    "Lien" means, with respect to the Company (or any other specified
                ----                                                            
Person):

               (a)  any lien, encumbrance, mortgage, pledge, charge or security
     interest of any kind upon any property or assets of the Company (or such
     specified Person), whether now owned or hereafter acquired, or upon the
     income or profits therefrom;

               (b)  the acquisition of, or the agreement to acquire, any
     property or asset upon conditional sale or subject to any other title
     retention agreement, device or arrangement (including a Capitalized Lease);

               (c)  the sale, assignment, pledge or transfer for security of any
     accounts, general intangibles or chattel paper of the Company (or such
     specified Person), with or without recourse;

               (d)  the transfer of any tangible property or assets for the
     purpose of subjecting such items to the payment of previously outstanding
     Indebtedness in priority to payment of the general creditors of the Company
     (or such specified Person); and

               (e)  the existence for a period of more than 120 consecutive days
     of any Indebtedness against the Company (or such specified Person) which if
     unpaid would by law or upon a Bankruptcy Default be given any priority over
     general creditors.
 
     1.114.    "Loan" means, collectively, the Revolving Loan and the Canadian
                ----
Loan.
            
     1.115.    "Margin Stock" means "margin stock" within the meaning of
                ------------
Regulations T, U or X of the Board of Governors of the Federal Reserve System.

     1.116.    "Material Adverse Change" means, since any specified date or from
                -----------------------
the circumstances existing immediately prior to the happening of any specified
event, a material

                                      -21-
<PAGE>
 
adverse change in (a) the business, assets, financial condition, income or
prospects of the Company and its Subsidiaries (on a Consolidated basis), whether
as a result of (i) general economic conditions affecting the wireless
telecommunications industry, (ii) difficulties in obtaining supplies and raw
materials, (iii) fire, flood or other natural calamities, (iv) environmental
pollution, (v) regulatory changes, judicial decisions, war or other governmental
action or (vi) any other event or development, whether or not related to those
enumerated above or (b) the ability of the Obligors taken as a whole to perform
their material obligations under the Credit Documents or (c) the rights and
remedies of the Agent and the Lenders under the Credit Documents (to the extent
not caused by the gross negligence or willful misconduct of the Agent or the
Lenders).

     1.117.    "Material Agreements" is defined in Section 7.2.2.
                -------------------                              

     1.118.    "Material Financing Debt" means any Financing Debt (other than
                -----------------------
the Credit Obligations) outstanding in an aggregate amount of principal (whether
or not due) and accrued interest exceeding $500,000.

     1.119.    "Maximum Amount of Canadian Credit" is defined in Section 2.2.2.
                ---------------------------------                              

     1.120.    "Maximum Amount of Revolving Credit" is defined in Section 2.1.2.
                ----------------------------------                              

     1.121.    "Moody's" means Moody's Investors Service, Inc.
                -------                                       

     1.122.    "Mortgages" means the mortgages and the deeds of trust (and the
                ---------                                                     
leasehold mortgages and leasehold deeds of trust) executed by the Company or any
of its Subsidiaries in favor of the Agent for the benefit of the Lenders,
encumbering the real property or leaseholds upon which Towers are located, in
substantially the form of Exhibits 6.20.3A and 6.20.3B, respectively.

     1.123.    "Multiemployer Plan" means any Plan that is a "multiemployer
                ------------------
plan" as defined in section 4001(a)(3) of ERISA.

     1.124.    "Net Asset Sale Proceeds" means the cash proceeds of the sale or
                -----------------------                                        
disposition of assets (including by way of merger), and the cash proceeds of any
insurance payments on account of the destruction or loss of property, by the
Company or any of its Subsidiaries after the Initial Closing Date, net of (a)
any Indebtedness permitted by Section 6.6.7 (purchase money Indebtedness and
Capitalized Leases) secured by assets being sold in such transaction required to
be paid from such proceeds, (b) income taxes that, as estimated by the Company
in good faith, will be required to be paid by the Company or any of its
Subsidiaries in cash as a result of, and within 16 months after, such sale or
disposition, (c) reasonable reserves for liabilities, escrows and purchase price
adjustments resulting from the sale of assets and (d) all reasonable expenses of
the Company or any of its Subsidiaries payable in connection with the sale or
disposition; provided, however, that "Net Asset Sale Proceeds" shall not include
             --------  -------                                                  
cash proceeds:

                                      -22-
<PAGE>
 
                    (i)    of asset sales permitted by Section 6.11.1, 6.11.2
               and 6.11.8,

                    (ii)   of mergers permitted by Section 6.11.3 or

                    (iii)  in an amount not exceeding $250,000 in any fiscal
               year in the aggregate that will be used to acquire replacement or
               other assets within 180 days after such sale, disposition,
               destruction or loss; provided, however, that if any amount in
               this clause (iii) is not actually used to acquire replacement or
               other assets within such 180-day period, such amount shall become
               Net Asset Sale Proceeds.

     1.125.    "Net Debt Proceeds" means cash proceeds (net of reasonable 
                -----------------
out-of-pocket transaction fees and expenses) from the incurrence by the Company
or any of its Subsidiaries after the Initial Closing Date of Financing Debt
other than Financing Debt permitted by Sections 6.6.1 (the Loan), 6.6.7
(purchase money Indebtedness and Capitalized Leases), 6.6.8 (seller debt),
6.6.10 (intercompany Indebtedness), 6.6.11 (Senior Subordinated Debt and 6.6.14
(other Indebtedness).

     1.126.    "Net Equity Proceeds" means the cash proceeds (net of reasonable
                -------------------
out-of-pocket fees and expenses) received by the Company or any of its
Subsidiaries in connection with any issuance by the Company or any of its
Subsidiaries after the Initial Closing Date of any shares of its capital stock,
other equity interests or options, warrants or other purchase rights to acquire
such capital stock or other equity interests to, or receipt of a capital
contribution from, any Person (other than any Obligors or their officers,
employees and directors) other than warrants issued in connection with the
Senior Subordinated Notes.

     1.127.    "Nonperforming Lender" is defined in Section 10.4.4.
                --------------------                               

     1.128.    "Notes" means, collectively, the Revolving Notes and the Canadian
                -----                                                           
Note.

     1.129     "Obligor" means the Borrowers, the Company, each other Guarantor
               -------
and each other Person guaranteeing or providing collateral for the Credit
Obligations.

     1.130.    "Offering Memorandum" is defined in Section 7.2.1.
                -------------------                              

     1.131.    "Overdue Reimbursement Rate" means, at any date, the highest
                --------------------------                                 
Applicable Rate then in effect.

     1.132.    "Payment Date" means (a) the last Banking Day of each February,
                ------------
May, August and November, beginning on the first such date after the date hereof
and (b) the Final Maturity Date.

                                      -23-
<PAGE>
 
     1.133.    "PBGC" means the Pension Benefit Guaranty Corporation or any
                ----                                                       
successor entity.

     1.134.    "PCS A-F Block Provider" means (a) a licensee of personal
                ----------------------                                  
communications services frequencies who was licensed by the FCC (i) in auctions
of the A-block, B-block, D-block, E-block, or F-block frequencies concluded in
1995, 1996 and 1997 or (ii) in other auctions for which the field of bidders is
not restricted by size or other economic factors and (b) any Person holding any
such license acquired by assignment, disaggregation or partitioning subsequent
to such auction.

     1.135.    "PCS C-Block Provider" means (a) a licensee of 30 MHz personal
                --------------------                                         
communication services frequencies who was licensed by the FCC in the C-block
auction concluded in May 1996 and (b) any other licensee of personal
communications services frequencies who was licensed by the FCC in a special
auction restricted to small or disadvantaged businesses.

     1.136.    "Percentage Interest" means, with respect to any Lender, the
                -------------------                                        
Commitment of such Lender with respect to the respective portions of the Loan
and Letter of Credit Exposure. For purposes of determining votes or consents by
the Lenders, the Percentage Interest of any Lender shall be computed as follows:
(a) at all times when no Event of Default under Section 8.1.1 and no Bankruptcy
Default exists, the ratio that the respective Commitments of such Lender bears
to the total Commitments of all Lenders as from time to time in effect and
reflected in the Register, and (b) at all other times, the ratio that the
respective amounts of the outstanding Loan and Letter of Credit Exposure owing
to such Lender bear to the total outstanding Loan and Letter of Credit Exposure
owing to all Lenders.

     1.137.    "Performing Lender" is defined in Section 10.4.4.
                -----------------                               

     1.138.    "Person" means any present or future natural person or any
                ------                                                   
corporation, association, partnership, joint venture, limited liability, joint
stock or other company, business trust, trust, organization, business or
government or any governmental agency or political subdivision thereof.

     1.139.    "PIK Interest" means any accrued interest payments on Financing
                ------------
Debt that are postponed or made through the issuance of "payment-in-kind" notes
or other similar securities (including book-entry accrual with respect to such
postponed interest payments), all in accordance with the terms of such Financing
Debt; provided, however, that in no event shall PIK Interest include payments
      --------  -------
made with cash or Cash Equivalents.

     1.140.    "Plan" means, at any date, any pension benefit plan subject to
                ----
Title IV of ERISA maintained, or to which contributions have been made or are
required to be made, by any ERISA Group Person within six years prior to such
date and any pension benefit plan subject to a similar statute under Canadian
law.

                                      -24-
<PAGE>
 
     1.141.    "Pledged Towers" means, on any date, Towers with respect to which
                --------------
the Lenders hold a perfected, first priority security interest in the Towers and
the real property or leasehold upon which such Towers are located and, in the
case of leaseholds, the Lenders have received an Estoppel and Consent Letter
from the lessor.

     1.142.    "RCRA" means the federal Resource Conservation and Recovery Act,
42 U.S.C. section 690, et seq. and any similar statute under Canadian law.
                       -- ---                                             

     1.143.    "Reference Total Leverage Ratio" means, on any date, the ratio of
                ------------------------------
(a) Consolidated Total Debt as of the end of the most recent period of four
consecutive fiscal quarters for which financial statements have been furnished
to the Lenders in accordance with Sections 6.4.1 and 6.4.2 prior to such date to
(b) Consolidated Adjusted EBITDA for such period.

     1.144.    "Register" is defined in Section 11.1.3.
                --------                               

     1.145.    "Related Fund" means, with respect to any Lender that is a fund
                ------------
that invests in senior bank loans, any other fund that invests in senior bank
loans and is managed by the same investment advisor as such Lender or by an
Affiliate of such investment advisor.

     1.146.    "Replacement Lender" is defined in Section 11.3.
                ------------------                             

     1.147.    "Required Lenders" means, with respect to any approval, consent,
                ----------------                                               
modification, waiver or other action to be taken by the Agent or the Lenders
under the Credit Documents which require action by the Required Lenders, such
Lenders as own at least two thirds of the Percentage Interests; provided,
                                                                -------- 
however, that with respect to any matters referred to in the proviso to Section
-------                                                                        
15.1, Required Lenders means such Lenders as own at least the respective
portions of the Percentage Interests required by Section 15.1.

     1.148.    "Revolving Loan" is defined in Section 2.1.4.
                --------------                              

     1.149.    "Revolving Notes" is defined in Section 2.1.4.
                ---------------                              

     1.150.    "S&P" means Standard & Poor's, a division of The McGraw Hill
                ---                                                        
Companies, Inc.

     1.151.    "Securities Act" means the federal Securities Act of 1933 and any
                --------------                                                  
similar statutes under Canadian law.

     1.152.    "Senior Subordinated Notes" means the Senior Subordinated
                -------------------------
Convertible Notes of the Company, dated June 1, 1998, issued in the original
principal amount of $15,000,000.

                                      -25-
<PAGE>
 
     1.153.    "Senior Subordinated Notes Purchase Agreement" means the Purchase
                --------------------------------------------                    
Agreement dated as of May 11, 1998, as in effect on the date hereof and as
subsequently amended in accordance with Section 6.2.4, between the Company and
the initial purchaser of the Senior Subordinated Notes.

     1.154.    "Subsidiary" means any Person of which the Company (or other
                ----------                                                 
specified Person) shall at the time, directly or indirectly through one or more
of its Subsidiaries, (a) own at least 50% of the outstanding capital stock (or
other shares of beneficial interest) entitled to vote generally, (b) hold at
least 50% of the partnership, joint venture or similar interests or (c) be a
general partner or joint venturer.

     1.155.    "Syndication Agent" means BancBoston Securities Inc., a Delaware
                -----------------                                              
corporation.

     1.156.    "Tax" means any present or future tax, levy, duty, impost,
                ---
deduction, withholding or other charges of whatever nature at any time required
by any Legal Requirement (a) to be paid by any Lender or (b) to be withheld or
deducted from any payment otherwise required hereby to be made to any Lender, in
each case on or with respect to its obligations hereunder, the Loan, any payment
in respect of the Credit Obligations or any Funding Liability not included in
the foregoing; provided, however, that the term "Tax" shall not include taxes
               --------  -------
imposed upon or measured by the net income of such Lender or franchise taxes
that are imposed in lieu of net income taxes; provided, further, however, that
                                              --------  -------  -------
the term "Tax" shall include withholding taxes in any event.

     1.157.    "Tower Cash Flow Availability" means, at any date, an amount
                ----------------------------
equal to the sum of (a) $15,000,000 plus (b) the product of:
                                    ----                    

                    (i)  Consolidated Annualized Tower Cash Flow for the most
               recently completed fiscal quarter for which financial statements
               have been furnished to the Lenders in accordance with Section
               6.4.1 or 6.4.2 prior to such date multiplied by
                                                 -------------

                    (ii) the percentage of (A) Consolidated Senior Debt divided
                                                                        -------
               by (B) Consolidated Adjusted EBITDA required by Section 6.5.2 as
               --
               of the end of such fiscal quarter.

     1.158.    "Tower Company" means a corporation or any other entity engaged
                -------------                                                 
primarily in the business of owning and/or operating Towers and leasing space
thereon to tenants.

     1.159.    "Towers" means towers for wireless telecommunications and
                ------
broadcast carriers.

     1.160.    "Tranche" means each of the Revolving Loan and the Canadian Loan,
                -------                                                         
considered as a separate credit facility.

                                      -26-
<PAGE>
 
     1.161.    "Uniform Customs and Practice" is defined in Section 2.4.6.
                ----------------------------                              

     1.162.    "United States Funds" means such coin or currency of the United
                -------------------                                           
States of America as at the time shall be legal tender therein for the payment
of public and private debts.

     1.163.    "U.S. Borrower" means Westower Holdings Ltd., a Wyoming
                -------------
 corporation.
 
     1.164.    "Wholly Owned Subsidiary" means any Subsidiary of which all of
                -----------------------
the outstanding capital stock (or other shares of beneficial interest) entitled
to vote generally (other than directors' qualifying shares and, in the case of
Foreign Subsidiaries, shares required by Legal Requirements to be held by
foreign nationals) is owned by the Company (or other specified Person) directly,
or indirectly through one or more Wholly Owned Subsidiaries.

2.   The Credits.
     ----------- 

     2.1       Revolving Credit.
               ---------------- 
 
               2.1.1.  Revolving Loan.  Subject to all the terms and conditions
     of this Agreement and so long as no Default exists, from time to time on
     and after the Initial Closing Date and prior to the Final Maturity Date the
     Lenders will, severally in accordance with their respective Commitments in
     the Revolving Loan, make loans to the U.S. Borrower in such amounts of
     United States Funds as may be requested by the U.S. Borrower in accordance
     with Section 2.1.3. The sum of the aggregate principal amount of loans made
     under this Section 2.1.1 at any one time outstanding plus the Letter of
                                                          ----
     Credit Exposure plus the Canadian Loan shall in no event exceed the lesser
                     ----
     of (a) Tower Cash Flow Availability or (b) the Maximum Amount of Revolving
     Credit. In no event will the principal amount of loans at any one time
     outstanding made by any Lender pursuant to this Section 2.1, together with
     such Lender's Percentage Interest in the Letter of Credit Exposure, exceed
     such Lender's Commitment with respect to the Revolving Loan.

               2.1.2.  Maximum Amount of Revolving Credit.  The term "Maximum
                       ----------------------------------             -------
     Amount of Revolving Credit" means, on any date, the lesser of (a) (i) the
     --------------------------
     amount specified opposite such date in the table below:

                         Period                     Amount
                         ------                     ------
 
               Prior to August 31, 2000..........  $75,000,000
 
               August 31, 2000 through
                November 29, 2000................  $72,187,500
 

                                      -27-
<PAGE>
 
               November 30, 2000 through
                February 27, 2001................  $69,375,000
 
               February 28, 2001 through
                May 30, 2001.....................  $66,562,500
 
               May 31, 2001 through
                August 30, 2001..................  $63,750,000
             
               August 31, 2001 through
                November 29, 2001................  $60,000,000
             
               November 30, 2001 through
                February 27, 2002................  $56,250,000
             
               February 28, 2002 through
                May 30, 2002.....................  $52,500,000
             
               May 31, 2002 through
                August 30, 2002..................  $48,750,000
             
               August 31, 2002 through
                November 29, 2002................  $45,000,000
             
               November 30, 2002 through
                February 27, 2003................  $41,250,000
             
               February 28, 2003 through
                May 30, 2003.....................  $37,500,000
             
               May 31, 2003 through
                August 30, 2003..................  $33,750,000
             
               August 31, 2003 through
                November 29, 2003................  $30,000,000
             
               November 30, 2003 through
                February 28, 2004................  $26,250,000
             
               February 29, 2004 through
                May 30, 2004.....................  $22,500,000
             
               May 31, 2004 through

                                      -28-
<PAGE>
 
                August 30, 2004..................  $18,750,000
             
               August 31, 2004 through
                November 29, 2004................  $14,062,500
             
               November 30, 2004 through
                February 27, 2005................  $ 9,375,000
             
               February 28, 2005 through
                April 24, 2005...................  $ 4,687,500
             
               Final Maturity Date...............  $         0

     minus (ii) Net Asset Sale Proceeds described in Section 4.2.3, Net Debt
     -----                                                                  
     Proceeds described in Section 4.2.4 and Net Equity Proceeds described in
     Section 4.2.5, in each case to the extent allocable to the Revolving Loan
     in accordance with Section 4.5.2, minus (iii) the amount of Consolidated
                                       -----                                 
     Excess Cash Flow described from time to time in Section 4.2.2 to the extent
     allocable to the Revolving Loan in accordance with Section 4.5.2, or (b)
     the amount (in an integral multiple of $1,000,000) to which the then
     applicable amount set forth in such table shall have been irrevocably
     reduced from time to time by notice from the U.S. Borrower to the Agent.
     The U.S. Borrower shall not give a notice reducing the amount applicable to
     any period in the table above unless it shall also reduce the amounts
     applicable to all subsequent periods in such table to at least the same
     specified lower amount, so that the Maximum Amount of Revolving Credit for
     any subsequent period shall not exceed the reduced Maximum Amount of
     Revolving Credit applicable to any prior period.

               2.1.3.  Borrowing Requests.  The U.S. Borrower may from time to
                       ------------------
     time request a loan under Section 2.1.1 by providing to the Agent an
     irrevocable notice (which may be given by a telephone call received by a
     Lending Officer if promptly confirmed in writing). Such notice must be not
     later than 1:00 p.m. (Boston time) on the first Banking Day (third Banking
     Day if any portion of such loan will be subject to a Eurodollar Pricing
     Option on the requested Closing Date) prior to the requested Closing Date
     for such loan. The notice must specify (a) the amount of the requested
     loan, which shall be not less than $1,000,000 and an integral multiple of
     $100,000 and (b) the requested Closing Date therefor, which shall be a
     Banking Day. Upon receipt of such notice, the Agent will promptly inform
     each other Lender (by telephone or otherwise). Each such loan will be made
     at the Boston Office by depositing the amount thereof to the general
     account of the U.S. Borrower with the Agent. In connection with each such
     loan, the U.S. Borrower shall furnish to the Agent a certificate in
     substantially the form of Exhibit 5.2.1.

               2.1.4.  Revolving Notes.  The aggregate principal amount of the
                       ---------------
     loans outstanding from time to time under this Section 2.1 is referred to
     as the "Revolving
             ---------

                                      -29-
<PAGE>
 
     Loan". The Agent shall keep a record of the Revolving Loan and the
     ----
     respective interests of the Lenders therein as part of the Register, which
     shall evidence the Revolving Loan. The Revolving Loan shall be deemed owed
     to each Lender having a Commitment therein severally in accordance with
     such Lender's Percentage Interest therein, and all payments thereon shall
     be for the account of each Lender in accordance with its Percentage
     Interest therein. Upon written request of any Lender, the U.S. Borrower's
     obligations to pay such Lender's Percentage Interest in the Revolving Loan
     shall be further evidenced by a separate note of the U.S. Borrower in
     substantially the form of Exhibit 2.1.4 (the "Revolving Notes"), payable to
                                                   ---------------
     such Lender in accordance with such Lender's Percentage Interest in the
     Revolving Loan.

               2.1.5.  Disproportionate Advances.
                       ------------------------- 

               (a)  In the event that a request for a loan under Section 2.2 or,
     at a time when the Canadian Loan is outstanding, this Section 2.1 would
     cause the outstanding portion of Credit Exposure owned by Paribas and
     Paribas Bank of Canada to exceed Paribas' Commitment, then the U.S.
     Borrower and the Lenders shall make such arrangements as shall be necessary
     so that the Lenders other than Paribas purchase assignments of the
     Revolving Loan from Paribas so that, after giving effect thereto, the
     portion of Credit Exposure owned by Paribas and Paribas Bank of Canada does
     not exceed Paribas' Commitment and the portion of the Revolving Loan that
     would have been owned by Paribas but for the provisions of this Section
     2.1.5 (a "Disproportionate Advance") shall be owned by the other Lenders in
               ------------------------
     accordance with their relative Percentage Interests in the Revolving Loan.
     Each Disproportionate Advance must be subject to a Eurodollar Pricing
     Option in accordance with the terms hereof with a Eurodollar Interest
     Period commencing no earlier than the date the Disproportionate Advance is
     created. In the event Eurodollar Pricing Options are for any reason not
     generally available to the Lenders, the interest on such Disproportionate
     Advance shall be computed based on the Base Rate.

               (b)  Each Lender irrevocably agrees to make such Disproportionate
     Advance in the amount and in the manner specified above in this Section
     2.1.5, notwithstanding (a) whether any conditions specified in Section 5
     have been satisfied, (b) that a Default or an Event of Default has occurred
     and is continuing or (c) the date of such Disproportionate Advance.  In the
     event that any Disproportionate Advance cannot for any reason be made on
     the date required above (including as a result of the commencement of a
     proceeding under the Bankruptcy Code), each Lender shall promptly purchase
     from  Paribas as of the date the Disproportionate Advance otherwise would
     have occurred such participation in the Disproportionate Advance as shall
     be necessary to cause the Lenders (other than Paribas) to share in the
     Disproportionate Advance ratably based upon their respective Percentage
     Interests in the Revolving Loan.  In the event of such participations, all
     interest payable on the Disproportionate Advance shall be for the account
     of  Paribas until the date on which the participations are required to be
     purchased and, to the extent 

                                      -30-
<PAGE>
 
     attributable to the purchased participations, shall be payable to the
     participants from and after such date. At the time any such purchase of
     participations is actually made, the purchasing Lender shall pay Paribas
     interest on the principal amount of the participation purchased at the
     overnight Federal Funds Rate for each day, commencing with the date the
     Disproportionate Advance otherwise would have occurred to the date of
     payment for such participation.

           (c)   Each Disproportionate Advance shall be considered part of the
     Revolving Loan in all respects, with Percentage Interests of the Lenders
     therein to be different from their Percentage Interests in the balance of
     the Revolving Loan.  Each Disproportionate Advance shall remain outstanding
     until repaid by the U.S. Borrower; provided, however, that a
                                        --------  -------        
     Disproportionate Advance must be repaid by the U.S. Borrower at the end of
     a Eurodollar Interest Period with respect thereto if at such time the U.S.
     Borrower may request a borrowing under Section 2.1 in an amount sufficient
     to repay the Disproportionate Advance without causing the portion of Credit
     Exposure owned by Paribas and Paribas Bank of Canada to exceed Paribas'
     Commitment.

     2.2.  Canadian Credit.
           --------------- 

           2.2.1. Canadian Loan. Subject to all the terms and conditions of this
                  -------------   
Agreement and so long as no Default exists, from time to time on and after the
Initial Closing Date and prior to the Final Maturity Date the Canadian Lender
will make extensions of credit for its own account to the Canadian Borrower in
such amounts of Canadian Funds as the Canadian Borrower shall request for
revolving loans in accordance with Section 2.2.3 or for drafts or bills of
exchange for acceptance as Bankers' Acceptances in accordance with Section 2.3.
The sum of (a) the aggregate principal amount of loans made under this Section
2.2 at any one time outstanding plus (b) the face amount of Bankers' Acceptances
                                ----
issued in accordance with Section 2.3 then outstanding shall in no event exceed
the Maximum Amount of Canadian Credit. The sum of the Canadian Loan plus the
Revolving Loan plus Letter of Credit Exposure shall in no event exceed the
lesser of (i) Tower Cash Flow Availability or (ii) the Maximum Amount of
Revolving Credit. In the event the advance of any extension of credit
constituting a portion of the Canadian Loan would cause the Credit Exposure
owned by Paribas and Paribas Bank of Canada to exceed Paribas' Commitment, the
U.S. Borrower and the Lenders shall create a Disproportionate Advance under
Section 2.1.5.

          2.2.2. Maximum Amount of Canadian Credit.  The term "Maximum Amount of
                 ---------------------------------             -----------------
Canadian Credit" means, on any date, the lesser of (a) (i) the amount specified
---------------                                                                
opposite such date in the table below:

                Period                              Amount       
                ------                              ------      
           Prior to August 31, 2000.............  $10,000,000

                                      -31-
<PAGE>
 
           August 31, 2000 through
              November 29, 2000.......  $ 9,625,000
 
           November 30, 2000 through
              February 27, 2001.......  $ 9,250,000
 
           February 28, 2001 through
              May 30, 2001............  $ 8,875,000
 
           May 31, 2001 through
              August 30, 2001.........  $ 8,500,000
 
           August 31, 2001 through
              November 29, 2001.......  $ 8,000,000
 
           November 30, 2001 through
              February 27, 2002.......  $ 7,500,000
 
           February 28, 2002 through
              May 30, 2002............  $ 7,000,000
 
           May 31, 2002 through
              August 30, 2002.........  $ 6,500,000
 
           August 31, 2002 through
              November 29, 2002.......  $ 6,000,000
 
           November 30, 2002 through
              February 27, 2003.......  $ 5,500,000
 
           February 28, 2003 through
              May 30, 2003............  $ 5,000,000
 
           May 31, 2003 through
              August 30, 2003.........  $ 4,500,000
 
           August 31, 2003 through
              November 29, 2003.......  $ 4,000,000
 
           November 30, 2003 through
              February 28, 2004.......  $ 3,500,000
 
           February 29, 2004 through

                                      -32-
<PAGE>
 
              May 30, 2004............  $ 3,000,000
 
           May 31, 2004 through
              August 30, 2004.........  $ 2,500,000
 
           August 31, 2004 through
              November 29, 2004.......  $ 1,875,000
 
           November 30, 2004 through
              February 27, 2005.......  $ 1,250,000
 
           February 28, 2005 through
              April 24, 2005..........  $   625,000
 
           Final Maturity Date........  $         0

     minus (ii) Net Asset Sale Proceeds described in Section 4.2.3, Net Debt
     -----                                                                  
     Proceeds described in Section 4.2.4 and Net Equity Proceeds described in
     Section 4.2.5, in each case to the extent allocable to the Canadian Loan in
     accordance with Section 4.5.2, minus (iii) the amount of Consolidated
                                    -----                                 
     Excess Cash Flow described from time to time in Section 4.2.2 to the extent
     allocable to the Canadian Loan in accordance with Section 4.5.2, or (b) the
     amount (in an integral multiple of $1,000,000) to which the then applicable
     amount set forth in such table shall have been irrevocably reduced from
     time to time by notice from the Canadian Borrower to the Agent.  The
     Canadian Borrower shall not give a notice reducing the amount applicable to
     any period in the table above unless it shall also reduce the amounts
     applicable to all subsequent periods in such table to at least the same
     specified lower amount, so that the Maximum Amount of Canadian Credit for
     any subsequent period shall not exceed the reduced Maximum Amount of
     Canadian Credit applicable to any prior period.

          2.2.3. Borrowing Requests. The Canadian Borrower may from time to time
                 ------------------
     request a loan under Section 2.2.1 by providing to the Canadian Lender and
     the Agent an irrevocable notice (which may be given by a telephone call
     received by a Lending Officer if promptly confirmed in writing). Such
     notice must be not later than 1:00 p.m. (Toronto time) on the first Banking
     Day prior to the requested Closing Date for such loan. The notice must
     specify (a) the amount in Canadian Funds of the requested loan, which shall
     be not less than C$1,000,000 in Canadian Funds and an integral multiple of
     C$100,000 in Canadian Funds and (b) the requested Closing Date therefor,
     which shall be a Banking Day. Each such loan will be made at the Canadian
     Office by depositing the amount thereof to the general account of the
     Canadian Borrower with the Canadian Lender. In connection with each such
     loan, the Canadian Borrower shall furnish to the Canadian Lender and the
     Agent a certificate in substantially the form of Exhibit 5.2.1.

                                      -33-
<PAGE>
 
          2.2.4. Canadian Note.  The Agent shall keep a record of the Canadian
                 -------------                                                
Loan as part of the Register, which shall evidence the Canadian Loan.  The
Canadian Loan shall be owed to the Canadian Lender for its own account, and all
payments thereon shall be for the account of the Canadian Lender.  Upon written
request of the Canadian Lender, the Canadian Borrower's obligations to pay the
Canadian Lender shall be further evidenced by a note of the Canadian Borrower in
substantially the form of Exhibit 2.2.4 (the "Canadian Note").
                                              -------------   

     2.3.  Bankers' Acceptances.
           -------------------- 

           2.3.1. Requests for Bankers' Acceptances.  The Canadian Borrower may
                  ---------------------------------                            
from time to time request an extension of credit by the Canadian Lender through
the acceptance of Bankers' Acceptances by providing to the Canadian Lender and
the Agent an irrevocable notice (which may be given by a telephone call received
by a Lending Officer if promptly confirmed in writing).  Such notice must be not
later than 1:00 p.m. (Toronto time) on the first Banking Day prior to the
requested Closing Date for such extension of credit.  The notice must specify
(a) the amount in Canadian Funds of the requested extension of credit, which
shall be not less than C$1,000,000 in Canadian Funds and an integral multiple of
C$100,000 in Canadian Funds and (b) the requested Closing Date therefor, which
shall be a Banking Day.  In connection with each such extension of credit, the
Canadian Borrower shall furnish to the Canadian Lender and the Agent a
certificate in substantially the form of Exhibit 5.2.1.

           2.3.2. Form of Bankers' Acceptances.  To facilitate the acceptance of
                  ----------------------------                                  
Bankers' Acceptances hereunder, the Canadian Borrower shall from time to time,
as required by the Canadian Lender, provide the Canadian Lender with an
appropriate number of executed drafts drawn in blank by the Canadian Borrower in
the form prescribed from time to time by the Canadian Lender.

           The Canadian Borrower may, at its option, execute any draft by the
facsimile signature of any authorized signing officer of the Canadian Borrower,
and the Canadian Lender is authorized to accept or pay, as the case may be, any
draft of the Canadian Borrower which purports to bear such facsimile signature,
notwithstanding that any such individual has ceased to be an authorized signing
officer of the Canadian Borrower. Any such draft or Bankers' Acceptance shall be
as valid as if the individual were an authorized signing officer of the Canadian
Borrower at the date of issuance of such Bankers' Acceptance. Any such draft or
Bankers' Acceptance may be treated by the Canadian Lender for all purposes, and
shall bind the Canadian Borrower, as if duly signed in the signing officer's own
handwriting and issued by the Canadian Borrower. The Canadian Lender shall not
be liable for its failure to accept a Bankers' Acceptance as required hereunder
if the case of such failure is, in whole or in part, due to the failure of the
Canadian Borrower to provide executed drafts to the Canadian Lender on a timely
basis.

                                      -34-
<PAGE>
 
          The receipt by the Canadian Lender of a request for an extension of
     credit by way of Bankers' Acceptances shall be sufficient authority for the
     Canadian Lender to complete, and the Canadian Lender shall complete,
     subject to the terms and conditions of this Agreement, the pre-signed forms
     of drafts in accordance with such request, and the drafts so completed
     shall thereupon be deemed to have been presented for acceptance.

          2.3.3. Sale of Bankers' Acceptances.  For each extension of credit by
                 ----------------------------                                  
     way of Bankers' Acceptances, the Canadian Lender shall arrange, in
     accordance with normal market practice, for the sale on the Drawdown Date
     of the Bankers' Acceptances issued by the Canadian Borrower and to be
     accepted by the Canadian Lender, failing which the Canadian Lender shall
     purchase its Bankers' Acceptances at the BA Discount Rate.

          The Canadian Lender will make BA Discount Proceeds received by it
     available to the Canadian Borrower on the Drawdown Date by crediting the
     general account of the Canadian Borrower with the Canadian Lender.

          Notwithstanding the foregoing, if in the reasonable determination of
     the Canadian Lender a market for Bankers' Acceptances does not exist at any
     time, or the Canadian Lender cannot for other reasons readily sell Bankers'
     Acceptances or perform its other obligations under this Agreement with
     respect to Bankers' Acceptances, then upon written notice by the Canadian
     Lender to the Canadian Borrower, the Canadian Borrower's right to request
     extensions of credit by way of Bankers' Acceptances shall be suspended
     until the Canadian Lender notifies the Canadian Borrower that any condition
     causing such determination no longer exists.

          2.3.4. Size and Maturity of Bankers' Acceptances and Rollovers.  Each
                 -------------------------------------------------------       
advance of Bankers' Acceptances shall be in a minimum amount of C$1,000,000 in
Canadian Funds and in whole multiples of C$100,000 in Canadian Funds, and each
Bankers' Acceptance shall be in the amount of C$100,000 in Canadian Funds or
whole multiples thereof.  Each Bankers' Acceptance shall have a term which is
approximately one, two, three or six months after the date of acceptance of the
draft by the Canadian Lender.  At no time shall Bankers' Acceptances be
outstanding with more than eight different maturity dates.  No Bankers'
Acceptance may mature on a date which is not a Banking Day, or on a date which
is later than the Final Maturity Date.  Upon maturity of a Bankers' Acceptance
the face amount may be renewed as a Bankers' Acceptance or may be converted into
a revolving loan under Section 2.2 with interest at the Applicable Rate computed
on the basis of the Canadian Prime Rate.

          2.3.5. Payment of Bankers' Acceptances.  The Canadian Borrower shall
                 -------------------------------                              
provide (by arranging a rollover or conversion in accordance with this
Agreement, or otherwise) for payment to the Canadian Lender of the full face
amount of such Bankers' Acceptance on the earlier of (a) the maturity date of a
Bankers' Acceptance and (b) the date on which the Credit Obligations become due
and payable pursuant to Section 4.1 or,

                                      -35-
<PAGE>
 
in the case of clause (a) above, if the Canadian Borrower fails to do so and is
otherwise entitled to an extension of credit under Section 2.2, the amount shall
be deemed to be a revolving loan under Section 2.2 with interest at the
Applicable Rate computed on the basis of the Canadian Prime Rate. The Canadian
Lender shall be entitled to recover interest from the Canadian Borrower at a
rate per annum equal to the Applicable Rate computed on the basis of the
Canadian Prime Rate, compounded monthly, on any amount which has not been paid
by the Canadian Borrower in accordance with this Section 2.3.5. Interest shall
be calculated from and including the date of maturity of a Bankers' Acceptance
up to but excluding the date such payment, and all interest thereon (both before
and after demand, default and judgment), is paid by the Canadian Borrower.

          2.3.6. Waiver. The Canadian Borrower shall not claim from the Canadian
                 ------
Lender any days of grace for the payment at maturity of any Bankers' Acceptances
presented and accepted by the Canadian Lender pursuant to this Agreement. The
Canadian Borrower waives any defense to payment arising solely from the fact
that a Bankers' Acceptance shall be held by the Canadian Lender in its own right
at the maturity thereof, and the doctrine of merger shall not apply to any
Bankers' Acceptance that is at any time held by the Canadian Lender in its own
right.

          2.3.7  Degree of Care.  Any executed drafts to be used as Bankers'
                 --------------                                             
Acceptances which are delivered to the Canadian Lender shall be held in
safekeeping with the same degree of care as if they were the Canadian Lender's
own property, and shall be kept at the place where such drafts are ordinarily
held by such Canadian Lender.

          2.3.8. Indemnity. The Canadian Borrower shall indemnify and hold the
                 ---------
Canadian Lender harmless from any loss, cost, damage or expense with respect to
any Bankers' Acceptance dealt with by the Canadian Lender, but shall not be
obligated to indemnify the Canadian Lender for any loss, costs, damage or
expense caused by the gross negligence or willful misconduct of the Canadian
Lender.

          2.3.9  Obligations Absolute.  The obligations of the Canadian Borrower
                 --------------------                                           
with respect to Bankers' Acceptances under this Agreement shall be unconditional
and irrevocable, and shall be paid strictly in accordance with this Agreement
under all circumstances, including the following:

          (a)  any lack of validity or enforceability of any draft accepted by
     the Canadian Lender as a Bankers' Acceptance; or

          (b)  the existence of any claim, set-off, defense or other right
     which the Canadian Borrower may have at any time against the holder of a
     Bankers' Acceptance, the Canadian Lender or any other Person, whether in
     connection with this Agreement or otherwise.

                                      -36-
<PAGE>
 
          2.3.10.  Depository Bills and Notes Act.  If the proposed Depository
                   ------------------------------                             
Bills and Notes Act is enacted in substantially the terms of Bill S-9, to which
first reading was given in the House of Commons of Canada on March 25, 1998, all
Bankers' Acceptances accepted by the Canadian Lender under this Agreement after
the effective date of such Act and after clearing services acceptable to the
Canadian Borrower and the Canadian Lender are available, shall be issued in the
form of a "depository bill" and deposited with a "clearing house," as those
terms are defined in such Act.  At that time, the Canadian Lender shall
establish such procedures, consistent with the terms of this Agreement and the
requirements of such Act, as are reasonably necessary to accomplish the parties'
intention.

          2.3.11.  Prohibited Use of Bankers' Acceptances. The Canadian Borrower
                   --------------------------------------
shall not enter into any agreement or arrangement of any kind with any Person to
whom Bankers' Acceptances have been delivered whereby the Canadian Borrower
undertakes to replace such Bankers' Acceptances on a continuing basis with other
Bankers' Acceptances, nor shall the Canadian Borrower directly or indirectly
take, use or provide Bankers' Acceptances as security for loans or advances from
any other Person.

2.4.      Letters of Credit.
          ----------------- 

          2.4.1. Issuance of Letters of Credit.  Subject to all the terms and
                 -----------------------------                               
conditions of this Agreement and so long as no Default exists, from time to time
on and after the Initial Closing Date and prior to the date five Banking Days
preceding the Final Maturity Date, the Letter of Credit Issuer will issue for
the account of the U.S.  Borrower one or more irrevocable documentary or standby
letters of credit in United States Funds (the "Letters of Credit").  The sum of
                                               -----------------               
Letter of Credit Exposure plus the Revolving Loan plus the Canadian Loan shall
                          ----                    ----                        
in no event exceed the lesser of (a) Tower Cash Flow Availability or (b) the
Maximum Amount of Revolving Credit.  Letter of Credit Exposure shall in no event
exceed $10,000,000.

          2.4.2. Requests for Letters of Credit. The U.S. Borrower may from time
                 ------------------------------
to time request a Letter of Credit to be issued by providing to the Letter of
Credit Issuer (and the Agent if the Letter of Credit Issuer is not the Agent) a
notice which is actually received not less than five Banking Days (for standby
Letters of Credit) and one Banking Day (for documentary Letters of Credit) prior
to the requested Closing Date for such Letter of Credit specifying (a) the
amount of the requested Letter of Credit, (b) the beneficiary thereof, (c) the
requested Closing Date and (d) a summary of the principal terms of the text for
such Letter of Credit. Each Letter of Credit will be issued by forwarding it to
the U.S. Borrower or to such other Person as directed in writing by the U.S.
Borrower. In connection with the issuance of any Letter of Credit, the U.S.
Borrower shall furnish to the Letter of Credit Issuer (and the Agent if the
Letter of Credit Issuer is not the Agent) a certificate in substantially the
form of Exhibit 5.2.1 and any customary application forms required by the Letter
of Credit Issuer. In the event of any

                                      -37-
<PAGE>
 
inconsistency between such application forms and this Agreement, this Agreement
shall govern.

          2.4.3. Form and Expiration of Letters of Credit. Each Letter of Credit
                 ----------------------------------------
issued under this Section 2.4 and each draft accepted or paid under such a
Letter of Credit shall be issued, accepted or paid, as the case may be, by the
Letter of Credit Issuer at its principal office. No Letter of Credit shall
provide for the payment of drafts drawn thereunder, and no draft shall be
payable, at a date which is later than the earlier of (a) the date 12 months
after the date of issuance (which expiration date may be extended at the option
of the Letter of Credit Issuer for additional 12-month periods ending prior to
the date referred to in clause (b) below) or (b) five Banking Days prior to the
Final Maturity Date. Each Letter of Credit and each draft accepted under a
Letter of Credit shall be in such form and minimum amount, and shall contain
such terms, as the Letter of Credit Issuer and the U.S. Borrower may agree upon
at the time such Letter of Credit is issued.

          2.4.4. Lenders' Participation in Letters of Credit.  Upon the issuance
                 -------------------------------------------                    
of any Letter of Credit, a participation therein, in an amount equal to each
Lender's Percentage Interest in the Revolving Loan, shall automatically be
deemed granted by the Letter of Credit Issuer to each such Lender on the date of
such issuance and such Lenders shall automatically be obligated, as set forth in
Section 10.4, to reimburse the Letter of Credit Issuer to the extent of their
respective Percentage Interests in the Revolving Loan for all obligations
incurred by the Letter of Credit Issuer to third parties in respect of such
Letter of Credit not reimbursed by the U.S. Borrower.  In the event the issuance
of such Letter of Credit would cause the Credit Exposure owned by  Paribas and
Paribas Bank of Canada to exceed  Paribas' Commitment, the U.S. Borrower and the
Lenders shall create a Disproportionate Advance under Section 2.1.5.  The Letter
of Credit Issuer will send to each Lender (and the Agent if the Letter of Credit
Issuer is not the Agent) a confirmation regarding the participations in Letters
of Credit outstanding during such month.

          2.4.5. Reimbursement of Payment.  At such time as a Letter of Credit
                 ------------------------                                     
Issuer makes any payment on a draft presented or accepted under a Letter of
Credit, the amount of such payment shall be considered a loan under Section
2.1.1 (regardless of whether the conditions set forth in Section 5.2 are
satisfied) and part of the Revolving Loan as if the U.S. Borrower had paid in
full the amount required with respect to the Letter of Credit by borrowing such
amount under Section 2.1.1, except as provided below.  In the event such amount
would cause the Revolving Loan to exceed the Maximum Amount of Credit or in the
event the Agent has previously provided written notice to the U.S. Borrower that
Letter of Credit payments will no longer be considered loans under Section
2.1.1, the U.S. Borrower will on demand pay to the Agent in immediately
available funds the amount of such payment.

          2.4.6. Uniform Customs and Practice.  The Uniform Customs and Practice
                 ----------------------------                                   
for Documentary Credits (1993 Revision), International Chamber of Commerce
Publication

                                      -38-
<PAGE>
 
No. 500, and any subsequent revisions thereof approved by a Congress of the
International Chamber of Commerce and adhered to by the Letter of Credit Issuer
(the "Uniform Customs and Practice"), shall be binding on the U.S. Borrower and
      ----------------------------
the Letter of Credit Issuer except to the extent otherwise provided herein, in
any Letter of Credit or in any other Credit Document. Anything in the Uniform
Customs and Practice to the contrary notwithstanding:

           (a)   Neither the U.S. Borrower nor any beneficiary of any Letter of
     Credit shall be deemed an agent of any Letter of Credit Issuer.

           (b)   With respect to each Letter of Credit, neither the Letter of
     Credit Issuer nor its correspondents shall be responsible for or shall have
     any duty to ascertain (unless the Letter of Credit Issuer or such
     correspondent is grossly negligent or willful in failing so to ascertain):

                 (i)    the genuineness of any signature or the validity, form,
          sufficiency, accuracy, genuineness or legal effect of any
          endorsements;

                 (ii)   delay in giving, or failure to give, notice of arrival,
          notice of refusal of documents or of discrepancies in respect of which
          any Letter of Credit Issuer refuses the documents or any other notice,
          demand or protest;

                 (iii)  the performance by any beneficiary under any Letter of
          Credit of such beneficiary's obligations to the U.S. Borrower;

                 (iv)   inaccuracy in any notice received by the Letter of
          Credit Issuer;

                 (v)    the validity, form, sufficiency, accuracy, genuineness
          or legal effect of any instrument, draft, certificate or other
          document required by such Letter of Credit to be presented before
          payment of a draft if such instrument, draft, certificate or other
          document appears on its face to comply with the requirements of the
          Letter of Credit, or the office held by or the authority of any Person
          signing any of the same; or

                 (vi)   failure of any instrument to bear any reference or
          adequate reference to such Letter of Credit, or failure of any Person
          to note the amount of any instrument on the reverse of such Letter of
          Credit or to surrender such Letter of Credit or to forward documents
          in the manner required by such Letter of Credit.

          (c)    Except insofar as a particular Letter of Credit contains
     express, contrary instructions, the Letter of Credit Issuer may honor as
     complying with the terms of any Letter of Credit and with this Agreement
     any drafts or other documents otherwise in order

                                      -39-
<PAGE>
 
     signed or issued by an administrator, executor, conservator, trustee in
     bankruptcy, debtor in possession, assignee for benefit of creditors,
     liquidator, receiver or other legal representative of the party authorized
     under such Letter of Credit to draw or issue such drafts or other
     documents.

          (d)  The occurrence of any of the events referred to in the Uniform
     Customs and Practice or in the preceding clauses of this Section 2.4.6
     shall not affect or prevent the vesting of any of the Letter of Credit
     Issuer's rights or powers hereunder or the U.S. Borrower's obligation to
     make reimbursement of amounts paid under any Letter of Credit or any draft
     accepted thereunder.

           (e)   The U.S. Borrower will promptly examine (i) each Letter of
     Credit (and any amendments thereof) sent to it by the Letter of Credit
     Issuer and (ii) all instruments and documents delivered to it from time to
     time by the Letter of Credit Issuer.  The U.S. Borrower will promptly
     notify the Letter of Credit Issuer of any claim of noncompliance, the U.S.
     Borrower being deemed to have waived any such claim against such Letter of
     Credit Issuer and its correspondents unless such notice is given.  The
     Letter of Credit Issuer shall have no obligation or responsibility to send
     any such Letter of Credit or any such instrument or document to the U.S.
     Borrower.

          (f)  In the event of any conflict between the provisions of this
     Agreement and the Uniform Customs and Practice, the provisions of this
     Agreement shall govern.

          2.4.7.   Subrogation.  Upon any payment by a Letter of Credit Issuer
                   -----------                                                
under any Letter of Credit and until the reimbursement of such Letter of Credit
Issuer by the U.S. Borrower with respect to such payment, the Letter of Credit
Issuer shall be entitled to be subrogated to, and to acquire and retain, the
rights which the Person to whom such payment is made may have against the U.S.
Borrower, all for the benefit of the Lenders. The U.S. Borrower will take such
action as the Letter of Credit Issuer may reasonably request, including
requiring the beneficiary of any Letter of Credit to execute such documents as
the Letter of Credit Issuer may reasonably request, to assure and confirm to the
Letter of Credit Issuer such subrogation and such rights, including the rights,
if any, of the beneficiary to whom such payment is made in accounts receivable,
inventory and other properties and assets of any Obligor.

          2.4.8.   Modification, Consent, etc.  If the U.S. Borrower requests or
                   --------------------------                                   
consents in writing to any modification or extension of any Letter of Credit, or
waives any failure of any draft, certificate or other document to comply with
the terms of such Letter of Credit, and if the Letter of Credit Issuer consents
thereto, the Letter of Credit Issuer shall be entitled to rely on such request,
consent or waiver.  This Agreement shall be binding upon the U.S. Borrower with
respect to such Letter of Credit as so modified or extended, and with respect to
any action taken or omitted by such Letter of Credit Issuer pursuant to any such
request, consent or waiver.

                                      -40-
<PAGE>
 
     2.5   Application of Proceeds.
           ----------------------- 

          2.5.1   Revolving Loan.  Subject to Section 2.5.4, the U.S. Borrower
                  --------------                                              
     will apply the proceeds of the Revolving Loan for the acquisition of Towers
     and Tower Companies and construction of Towers, working capital and other
     lawful corporate purposes of the Company and its Subsidiaries.

          2.5.2   Canadian Loan. Subject to Section 2.5.4, the Canadian Borrower
                  -------------
     will apply the proceeds of the Canadian Loan for the acquisition of Towers
     and Tower Companies and construction of Towers, working capital and other
     lawful corporate purposes of the Company and its Subsidiaries.

          2.5.3   Letters of Credit.  Letters of Credit shall be issued only to
                  -----------------                                            
     provide credit support for payment or performance obligations related to
     the acquisition of Towers and Tower Companies or construction of Towers or
     for such other lawful corporate purposes as the U.S. Borrower has requested
     in writing and to which the Letter of Credit Issuer agrees.

          2.5.4   Specifically Prohibited Applications.  The Borrowers will not,
                  ------------------------------------                          
     directly or indirectly, apply any part of the proceeds of any extension of
     credit made pursuant to the Credit Documents to purchase or to carry Margin
     Stock or to any transaction prohibited by the Credit Documents or by Legal
     Requirements applicable to the Lenders.

     2.6   Nature of Obligations of Lenders to Make Extensions of Credit.  The
           -------------------------------------------------------------      
Lenders' obligations to extend credit under this Agreement are several and are
not joint or joint and several.  If on any Closing Date any Lender shall fail to
perform its obligations under this Agreement, the aggregate amount of
Commitments to make the extensions of credit under this Agreement shall be
reduced by the amount of unborrowed Commitment of the Lender so failing to
perform and the Percentage Interests shall be appropriately adjusted.  Lenders
that have not failed to perform their obligations to make the extensions of
credit contemplated by Section 2 may, if any such Lender so desires, assume, in
such proportions as such Lenders may agree, the obligations of any Lender who
has so failed and the Percentage Interests shall be appropriately adjusted.  The
provisions of this Section 2.6 shall not affect the rights of the Borrowers
against any Lender failing to perform its obligations hereunder.

 3.  Interest; Eurodollar Pricing Options; Fees.
     ------------------------------------------ 

     3.1   Interest.  The Loan (other than the portion of the Canadian Loan
           --------                                                        
subject to Bankers' Acceptances) shall accrue and bear interest at a rate per
annum which shall at all times equal the Applicable Rate.  Prior to any stated
or accelerated maturity of the Loan, on each Payment Date, (a) the U.S. Borrower
will pay the accrued and unpaid interest on the portion of the Revolving Loan
which was not subject to a Eurodollar Pricing Option and (b) the Canadian

                                      -41-
<PAGE>
 
Borrower will pay the accrued and unpaid interest on the portion of the Canadian
Loan which was not subject to Bankers' Acceptances.  On the last day of each
Eurodollar Interest Period or on any earlier termination of any Eurodollar
Pricing Option, the U.S. Borrower will pay the accrued and unpaid interest on
the portion of the Revolving Loan which was subject to the Eurodollar Pricing
Option which expired or terminated on such date.  In the case of any Eurodollar
Interest Period longer than three months, the U.S. Borrower will also pay the
accrued and unpaid interest on the portion of the Revolving Loan subject to the
Eurodollar Pricing Option having such Eurodollar Interest Period at three-month
intervals, the first such payment to be made on the last Banking Day of the
three-month period which begins on the first day of such Eurodollar Interest
Period.  On the stated or any accelerated maturity of the Loan, (i) the U.S.
Borrower will pay all accrued and unpaid interest on the Revolving Loan,
including any accrued and unpaid interest on any portion of the Loan which is
subject to a Eurodollar Pricing Option and (ii) the Canadian Borrower will pay
all accrued and unpaid interest on the portion of the Canadian Loan which is not
subject to Bankers' Acceptances.  Upon the occurrence and during the continuance
of an Event of Default, the Lenders may require accrued interest to be payable
on demand or at regular intervals more frequent than each Payment Date.  All
payments of interest hereunder shall be made, in the case of the Revolving Loan,
to the Agent for the account of each Lender in accordance with such Lender's
Percentage Interest therein and, in the case of the Canadian Loan, to the
Canadian Lender for its own account.

     3.2   Eurodollar Pricing Options.
           -------------------------- 

           3.2.1  Election of Eurodollar Pricing Options.  Subject to all of the
                  --------------------------------------                        
     terms and conditions hereof and so long as no Default exists, the U.S.
     Borrower may from time to time, by irrevocable notice to the Agent, such
     notice to be actually received by 1:00 p.m. (Boston time) not less than
     three Banking Days prior to the commencement of the Eurodollar Interest
     Period selected in such notice, elect to have such portion of the Revolving
     Loan as the U.S. Borrower may specify in such notice accrue and bear
     interest during the Eurodollar Interest Period so selected at the
     Applicable Rate computed on the basis of the Eurodollar Rate. In the event
     the U.S. Borrower at any time does not elect a Eurodollar Pricing Option
     under this Section 3.2.1 for any portion of the Revolving Loan (upon
     termination of a Eurodollar Pricing Option or otherwise), then such portion
     of the Revolving Loan will accrue and bear interest at the Applicable Rate
     based on the Base Rate. The U.S. Borrower shall elect to have each
     Disproportionate Advance to be subject to a Eurodollar Pricing Option at
     all times. No election of a Eurodollar Pricing Option shall become
     effective:

           (a)    if, prior to the commencement of any such Eurodollar Interest
     Period, the Agent reasonably determines that (i) the electing or granting
     of the Eurodollar Pricing Option in question would violate a Legal
     Requirement, (ii) Eurodollar deposits in an amount comparable to the amount
     of the Loan as to which such Eurodollar Pricing Option has been elected and
     which have a term corresponding to the proposed Eurodollar Interest Period
     are not readily available in the inter-bank Eurodollar market, or (iii) by

                                      -42-
<PAGE>
 
     reason of circumstances affecting the inter-bank Eurodollar market,
     adequate and reasonable methods do not exist for ascertaining the interest
     rate applicable to such deposits for the proposed Eurodollar Interest
     Period; or

           (b)    if the Required Lenders shall have advised the Agent by
     telephone or otherwise at or prior to noon (Boston time) on the second
     Banking Day prior to the commencement of such proposed Eurodollar Interest
     Period (and shall have subsequently confirmed in writing) that, after
     reasonable efforts to determine the availability of such Eurodollar
     deposits, the Required Lenders reasonably anticipate that Eurodollar
     deposits in an amount equal to the Percentage Interest of the Required
     Lenders in the portion of the Revolving Loan as to which such Eurodollar
     Pricing Option has been elected and which have a term corresponding to the
     Eurodollar Interest Period in question will not be offered in the
     Eurodollar market to the Required Lenders at a rate of interest that does
     not exceed the anticipated Eurodollar Basic Rate.

          3.2.2   Notice to Lenders and Borrowers. The Agent will promptly
                  ------------------------------- 
     inform each Lender (by telephone or otherwise) of each notice received by
     it from the U.S. Borrower pursuant to Section 3.2.1 for the Revolving Loan
     and of the Eurodollar Interest Period specified in such notice. Upon
     determination by the Agent of the Eurodollar Rate for such Eurodollar
     Interest Period or in the event such election shall not become effective,
     the Agent will promptly notify the U.S. Borrower and each Lender (by
     telephone or otherwise) of the Eurodollar Rate so determined or why such
     election did not become effective, as the case may be.

           3.2.3  Selection of Eurodollar Interest Periods.  Eurodollar Interest
                  ----------------------------------------                      
     Periods shall be selected so that:

           (a)    the minimum portion of the Loan subject to any Eurodollar
     Pricing Option shall be $1,000,000 and an integral multiple of $100,000, in
     each case in United States Funds;

           (b)    no more than 10 Eurodollar Pricing Options shall be
     outstanding at any one time;

           (c)    no Eurodollar Interest Period shall expire later than the
     Final Maturity Date; and

           (d)    prior to the earlier of the date 60 days after the Initial
     Closing Date or the date the Agent informs the Borrowers that the proposed
     initial syndication of the credit facilities provided hereby will close, no
     Eurodollar Interest Period shall extend beyond such date except with the
     written consent of the Agent.  The Borrowers and the Agent shall confer
     about the appropriate scheduling of the selection of Eurodollar Interest

                                      -43-
<PAGE>
 
     Periods to facilitate the anticipated syndication of the credit facilities
     provided herein to other Lenders.

          3.2.4   Additional Interest.  If any portion of the Loan subject to a
                  -------------------                                          
     Eurodollar Pricing Option is repaid, or any Eurodollar Pricing Option is
     terminated for any reason (including acceleration of maturity or in order
     to create a Disproportionate Advance) on a date which is prior to the last
     Banking Day of the Eurodollar Interest Period applicable to such Eurodollar
     Pricing Option, the U.S. Borrower will pay to the Agent for the account of
     each Lender in accordance with such Lender's Percentage Interest in the
     Revolving Loan, in addition to any amounts of interest otherwise payable
     hereunder, an amount equal to the present value (calculated in accordance
     with this Section 3.2.4) of interest for the unexpired portion of such
     Eurodollar Interest Period on the portion of the Revolving Loan so repaid,
     or as to which a Eurodollar Pricing Option was so terminated, at a per
     annum rate equal to the excess, if any, of (a) the Eurodollar Rate
     applicable to such Eurodollar Pricing Option minus (b) the rate of interest
                                                  -----
     obtainable by the Agent upon the purchase of debt securities customarily
     issued by the Treasury of the United States of America which have a
     maturity date approximating the last Banking Day of such Eurodollar
     Interest Period. The present value of such additional interest shall be
     calculated by discounting the amount of such interest for each day in the
     unexpired portion of such Eurodollar Interest Period from such day to the
     date of such repayment or termination at a per annum interest rate equal to
     the interest rate determined pursuant to clause (b) of the preceding
     sentence, and by adding all such amounts for all such days during such
     period. The determination by each affected Lender of such amount of
     interest shall, in the absence of manifest error, be conclusive. For
     purposes of this Section 3.2.4, if any portion of the Revolving Loan which
     was to have been subject to a Eurodollar Pricing Option is not outstanding
     on the first day of the Eurodollar Interest Period applicable to such
     Eurodollar Pricing Option other than for reasons described in Section 3.2.1
     or as a result of the failure of any Lender to perform its obligations
     under Section 2, the U.S. Borrower shall be deemed to have terminated such
     Eurodollar Pricing Option.

          3.2.5   Violation of Legal Requirements.  If any mandatory Legal
                  -------------------------------                         
     Requirement shall prevent any Lender from funding or maintaining through
     the purchase of deposits in the interbank Eurodollar market any portion of
     the Revolving Loan subject to a Eurodollar Pricing Option or otherwise from
     giving effect to such Lender's obligations as contemplated by Section 3.2,
     (a) the Agent may by notice to the U.S. Borrower terminate all of the
     affected Eurodollar Pricing Options, (b) the portion of the Revolving Loan
     subject to such terminated Eurodollar Pricing Options shall immediately
     bear interest thereafter at the Applicable Rate computed on the basis of
     the Base Rate and (c) the U.S. Borrower shall make any payment required by
     Section 3.2.4.

          3.2.6   Funding Procedure.  The Lenders may fund any portion of the
                  -----------------                                          
     Revolving Loan subject to a Eurodollar Pricing Option out of any funds
     available to the Lenders.

                                      -44-
<PAGE>
 
     Regardless of the source of the funds actually used by any of the Lenders
     to fund any portion of the Revolving Loan subject to a Eurodollar Pricing
     Option, however, all amounts payable hereunder, including the interest rate
     applicable to any such portion of the Revolving Loan and the amounts
     payable under Sections 3.2.4 and 3.5, shall be computed as if each Lender
     had actually funded such Lender's Percentage Interest in such portion of
     the Revolving Loan through the purchase of deposits in such amount of the
     type by which the Eurodollar Basic Rate was determined with a maturity the
     same as the applicable Eurodollar Interest Period relating thereto and
     through the transfer of such deposits from an office of the Lender having
     the same location as the applicable Eurodollar Office to one of such
     Lender's offices in the United States of America.

     3.3   Commitment Fees.  In consideration of the Lenders' commitments to
           ---------------                                                  
make the extensions of credit provided for in Section 2.1, while such
commitments are outstanding hereunder, the U.S. Borrower will pay to the Agent
for the account of the Lenders in accordance with the Lenders' respective
Commitments in the Revolving Loan, on each Payment Date, an amount equal to
interest computed at the Commitment Fee Rate on the amount by which (a) the
daily Maximum Amount of Revolving Credit during the three-month period or
portion thereof ending on such Payment Date exceeded (b) the sum of (i) the
daily Revolving Loan during such period or portion thereof plus (ii) daily
                                                           ----           
Letter of Credit Exposure during such period or portion thereof plus (iii) the
                                                                ----          
daily Canadian Loan during such period or portion thereof.

     3.4   Letter of Credit Fees.  The U.S. Borrower will pay to the Agent for
           ---------------------                                              
the account of each of the Lenders, in accordance with the Lenders' respective
Percentage Interests, on each Payment Date, a Letter of Credit fee equal to
interest at a rate per annum equal to the Applicable Margin indicated for the
Eurodollar Rate on the average daily Letter of Credit Exposure during the three-
month period or portion thereof ending on such Payment Date.  The U.S. Borrower
will pay to the Letter of Credit Issuer customary service charges and expenses
for its services in connection with the Letters of Credit at the times and in
the amounts from time to time in effect in accordance with its general rate
structure, including fees and expenses relating to issuance, amendment,
negotiation, cancellation and similar operations.

     3.5   Changes in Circumstances; Yield Protection.
           ------------------------------------------ 

          3.5.1   Reserve Requirements, etc.  If any Legal Requirement shall (a)
                  -------------------------                                     
     impose, modify, increase or deem applicable any insurance assessment,
     reserve, special deposit or similar requirement against any Funding
     Liability or the Letters of Credit, (b) impose, modify, increase or deem
     applicable any other requirement or condition with respect to any Funding
     Liability or the Letters of Credit, or (c) change the basis of taxation of
     Funding Liabilities or payments in respect of any Letter of Credit (other
     than changes in the rate of taxes measured by the overall net income of
     such Lender) and the effect of any of the foregoing shall be to increase
     the cost to any Lender of issuing, making, funding or maintaining its
     respective Percentage Interest in any portion of the Loan subject to a
     Eurodollar Pricing Option or any Letter of Credit, to reduce the amounts
     received or

                                      -45-
<PAGE>
 
     receivable by such Lender under this Agreement or to require such Lender to
     make any payment or forego any amounts otherwise payable to such Lender
     under this Agreement (other than any Tax or any reserves that are included
     in computing the Eurodollar Reserve Rate), then such Lender may claim
     compensation from the U.S. Borrower or the Canadian Borrower, as the case
     may be, under Section 3.5.5.

          3.5.2   Taxes.  All payments of the Credit Obligations shall be made
                  -----                                                       
     without set-off or counterclaim and free and clear of any deductions,
     including deductions for Taxes, unless the U.S. Borrower or the Canadian
     Borrower, as the case may be, is required by law to make such deductions.
     If (a) any Lender shall be subject to any Tax with respect to any payment
     of the Credit Obligations or its obligations hereunder or (b) the U.S.
     Borrower or the Canadian Borrower, as the case may be, shall be required to
     withhold or deduct any Tax on any payment on the Credit Obligations, then
     such Lender may claim compensation from such Borrower under Section 3.5.5
     to the extent such Lender is then in compliance with any applicable
     requirements of Section 13. Whenever Taxes must be withheld by either of
     the Borrowers with respect to any payments of the Credit Obligations, such
     Borrower shall promptly furnish to the Agent for the account of the
     applicable Lender official receipts (to the extent that the relevant
     governmental authority delivers such receipts) evidencing payment of any
     such Taxes so withheld. If such Borrower fails to pay any such Taxes when
     due or fails to remit to the Agent for the account of the applicable Lender
     the required receipts evidencing payment of any such Taxes so withheld or
     deducted, such Borrower shall indemnify the affected Lender for any
     incremental Taxes and interest or penalties that may become payable by such
     Lender as a result of any such failure. In the event any Lender receives a
     refund of any Taxes for which it has received payment from either of the
     Borrowers under this Section 3.5.2, such Lender shall promptly pay the
     amount of such refund to such Borrower, together with any interest thereon
     actually earned by such Lender.

          3.5.3   Capital Adequacy. If any Lender shall determine that
                  ----------------
     compliance by such Lender with any Legal Requirement regarding capital
     adequacy of banks or bank holding companies has or would have the effect of
     reducing the rate of return on the capital of such Lender and its
     Affiliates as a consequence of such Lender's commitment to make the
     extensions of credit contemplated hereby, or such Lender's maintenance of
     the extensions of credit contemplated hereby, to a level below that which
     such Lender could have achieved but for such compliance (taking into
     consideration the policies of such Lender and its Affiliates with respect
     to capital adequacy immediately before such compliance and assuming that
     the capital of such Lender and its Affiliates was fully utilized prior to
     such compliance) by an amount deemed by such Lender to be material, then
     such Lender may claim compensation from the U.S. Borrower or the Canadian
     Borrower, as the case may be, under Section 3.5.5.

          3.5.4   Regulatory Changes. If any Lender shall determine that (a) any
                  ------------------
     change in any Legal Requirement (including any new Legal Requirement) after
     the date hereof

                                      -46-
<PAGE>
 
     shall directly or indirectly (i) reduce the amount of any sum received or
     receivable by such Lender with respect to the Loan or the Letters of Credit
     or the return to be earned by such Lender on the Loan or the Letters of
     Credit, (ii) impose a cost on such Lender or any Affiliate of such Lender
     that is attributable to the making or maintaining of, or such Lender's
     commitment to make, its portion of the Loan or the Letters of Credit, or
     (iii) require such Lender or any Affiliate of such Lender to make any
     payment on, or calculated by reference to, the gross amount of any amount
     received by such Lender under any Credit Document (other than Taxes or
     income or franchise taxes), and (b) such reduction, increased cost or
     payment shall not be fully compensated for by an adjustment in the
     Applicable Rate or the Letter of Credit fees, then such Lender may claim
     compensation from the U.S. Borrower or the Canadian Borrower, as the case
     may be, under Section 3.5.5.

          3.5.5   Compensation Claims. Within 15 days after the receipt by
                  ------------------- 
     either of the Borrowers of a certificate from any Lender setting forth why
     it is claiming compensation under this Section 3.5 and computations (in
     reasonable detail) of the amount thereof, such Borrower shall pay to such
     Lender such additional amounts as such Lender sets forth in such
     certificate as sufficient fully to compensate it on account of the
     foregoing provisions of this Section 3.5, together with interest on such
     amount from the 15th day after receipt of such certificate until payment in
     full thereof at the Overdue Reimbursement Rate. The determination by such
     Lender of the amount to be paid to it and the basis for computation thereof
     hereunder shall be conclusive so long as (a) such determination is made in
     good faith, (b) no manifest error appears therein and (c) the Lender uses
     reasonable averaging and attribution methods. The Borrowers shall be
     entitled to replace any such Lender in accordance with Section 11.3.

          3.5.6   Mitigation. Each Lender shall take such commercially
                  ----------
     reasonable steps as it may determine are not disadvantageous to it,
     including changing lending offices to the extent feasible, in order to
     reduce amounts otherwise payable by either of the Borrowers to such Lender
     pursuant to Sections 3.2.4 and 3.5 or to make Eurodollar Pricing Options
     available under Sections 3.2.1 and 3.2.5. In addition, the Borrowers shall
     not be responsible for costs (a) under Section 3.5 arising more than 90
     days prior to receipt by the U.S. Borrower or the Canadian Borrower, as the
     case may be, of the certificate from the affected Lender pursuant to such
     Section 3.5 or (b) under Section 3.2.4 arising from the termination of
     Eurodollar Pricing Options more than 90 days prior to the demand by the
     Agent for payment under Section 3.2.4.

     3.6   Computations of Interest and Fees.  For purposes of this Agreement,
           ---------------------------------                                  
interest, commitment fees and Letter of Credit fees (and any other amount
expressed as interest or such fees) shall be computed on the basis of a 365-day
year; provided, however, that interest on any portion of the Loan subject to a
      --------  -------                                                       
Eurodollar Pricing Option shall be computed on the basis of a 360-day year for
actual days elapsed.  If any payment required by this Agreement becomes due on
any day that is not a Banking Day, such payment shall, except as otherwise
provided in the 

                                      -47-
<PAGE>
 
definition of "Eurodollar Interest Period", be made on the next succeeding
Banking Day. If the due date for any payment of principal is extended as a
result of the immediately preceding sentence, interest shall be payable for the
time during which payment is extended at the Applicable Rate.

4.   Payment.
     ------- 

     4.1   Payment at Maturity.  On the Final Maturity Date or any accelerated
           -------------------                                                
maturity of the Loan, the U.S. Borrower will pay to the Agent an amount equal to
the Revolving Loan then due and the Canadian Borrower will pay to the Canadian
Lender an amount equal to the Canadian Loan then due, in each case, together
with all accrued and unpaid interest and fees with respect thereto and all other
Credit Obligations then outstanding.

     4.2   Contingent Required Prepayments.
           ------------------------------- 

          4.2.1   Excess Credit Exposure.  If at any time the Revolving Loan
                  ----------------------                                    
     exceeds the limits set forth in Section 2.1, the U.S. Borrower shall within
     one Banking Day pay the amount of such excess to the Agent as a prepayment
     of the Revolving Loan. If at any time the Canadian Loan exceeds the limits
     set forth in Section 2.2, the Canadian Borrower shall within one Banking
     Day pay the amount of such excess to the Canadian Lender as a prepayment of
     the Canadian Loan (or, in the case of Bankers' Acceptances, deposit cash in
     the amount of such excess as provided in Section 4.5), and shall provide
     contemporaneous notice to the Agent; provided, however, that if the
                                          --------  -------
     Canadian Loan exceeds the limits set forth in Section 2.2 solely as a
     result of changes in the currency exchange rate as reported in accordance
     with Section 6.4.3, the Canadian Borrower shall prepay the amount of such
     excess (or, in the case of Bankers' Acceptances, deposit cash in the amount
     of such excess as provided in Section 4.5) within one Banking Day after the
     currency exchange report is required to be furnished to the Lenders in
     accordance with Section 6.4.3. If at any time the Letter of Credit Exposure
     exceeds the limits set forth in Section 2.3, the U.S. Borrower shall within
     one Banking Day pay the amount of such excess to the Agent to be applied as
     provided in Section 4.6.

          4.2.2   Excess Cash Flow. Within 120 days after the end of each fiscal
                  ----------------
     year ending on or after February 28, 2001, the Borrowers shall pay to the
     Agent as a prepayment of the Loan to be applied as provided in Section
     4.6.2 an amount equal to the lesser of (a) (i) 75% of Consolidated Excess
     Cash Flow for the Company's most recently completed fiscal year if the
     Reference Total Leverage Ratio is greater than 400%, or (ii) 50% of
     Consolidated Excess Cash Flow for the Company's most recently completed
     fiscal year if the Reference Total Leverage Ratio is less than or equal to
     400% for such fiscal year or (b) the amount of the Loan.

          4.2.3   Net Asset Sale Proceeds. Upon receipt by the Company or any of
                  ----------------------- 
     its Subsidiaries of Net Asset Sale Proceeds, the Borrowers shall within one
     Banking Day

                                      -48-
<PAGE>
 
     pay to the Agent as a prepayment of the Loan to be applied as provided in
     Section 4.6.2 the lesser of (a) the amount of such Net Asset Sale Proceeds
     or (b) the amount of the Loan.

          4.2.4   Net Debt Proceeds.  Upon receipt of Net Debt Proceeds by the
                  -----------------                                           
     Company or any of its Subsidiaries, the Borrowers shall within one Banking
     Day pay to the Agent as a prepayment of the Loan to be applied as provided
     in Section 4.6.2 the lesser of (a) the amount of such Net Debt Proceeds or
     (b) the amount of the Loan.

          4.2.5   Net Equity Proceeds. Upon receipt of Net Equity Proceeds by
                  -------------------
     the Company or any of its Subsidiaries, the Borrowers shall within one
     Banking Day pay to the Agent as a prepayment of the Loan to be applied as
     provided in Section 4.6.2 the lesser of (a) the amount of such Net Equity
     Proceeds or (b) the amount of the Loan.

     4.3   Voluntary Prepayments.  In addition to the prepayments required by
           ---------------------                                             
Section 4.2, either of the Borrowers may from time to time prepay all or any
portion of the Loan (in a minimum amount of $1,000,000 and an integral multiple
of $500,000, in United States Funds or Canadian Funds, as the case may be, or
such lesser amount as is then outstanding), without premium or penalty of any
type (except as provided in Section 3.2.4 with respect to the early termination
of Eurodollar Pricing Options or in Section 4.5 with respect to the early
payment of Bankers' Acceptances).  Such Borrower shall give the Agent (and the
Canadian Lender, in the case of the Canadian Loan) at least one Banking Day
prior notice of its intention to prepay the Revolving Loan or the Canadian Loan
under this Section 4.3, specifying the date of payment and the total amount of
the Revolving Loan or the Canadian Loan to be paid on such date.

     4.4   Letters of Credit.  If on the Final Maturity Date, any accelerated
           -----------------                                                 
maturity of the Credit Obligations or the date when Letter of Credit Exposure
exceeds the Maximum Amount of Revolving Credit, the Lenders shall be obligated
in respect of a Letter of Credit or a draft accepted under a Letter of Credit,
the U.S. Borrower will either:

           (a)    prepay such obligation by depositing cash with the Agent, or

           (b)    deliver to the Agent a standby letter of credit (designating
     the Letter of Credit Issuer as beneficiary and issued by a bank and on
     terms reasonably acceptable to the Letter of Credit Issuer),

in each case in an amount equal to all Letter of Credit Exposure (if then due
and payable) or the portion of Letter of Credit Exposure exceeding the Maximum
Amount of Revolving Credit (in other cases).  Any such cash so deposited and the
cash proceeds of any draw under any standby Letters of Credit so furnished,
including any interest thereon, shall be applied to reimburse payments by the
Letter of Credit Issuer on drafts presented or accepted under Letter of Credit,
and shall be returned by the Agent to the U.S. Borrower only when, and to the
extent that, the amount of such cash held by the Agent exceeds the Letter of
Credit Exposure at such time and no 

                                      -49-
<PAGE>
 
Default then exists. If the Credit Obligations become or are declared
immediately due and payable, the Agent may apply such cash, including any
interest thereon, to the payment of any of the Credit Obligations as provided in
section 3.5.6 of the Guarantee and Security Agreement.

     4.5   Bankers' Acceptances.  The Canadian Borrower shall pay to the
           --------------------                                         
Canadian Lender the full face amount of Bankers' Acceptances on the maturity
date thereof to the extent required by Section 2.3.5.  If on the Final Maturity
Date, any accelerated maturity of the Credit Obligations or the date when the
aggregate face amount of outstanding Bankers' Acceptances exceeds the Maximum
Amount of Canadian Credit, the Canadian Lender shall be obligated in respect of
a Bankers' Acceptance, the Canadian Borrower will prepay such obligation by
depositing cash in Canadian Funds with the Canadian Lender in an amount equal to
the full face amount of the outstanding Bankers' Acceptances (if then due and
payable) or the portion of Bankers' Acceptances exceeding the Maximum Amount of
Canadian Credit (in other cases), notwithstanding the fact that any of such
Bankers' Acceptances may be held by the Canadian Lender in its own right at
maturity.  Any cash so deposited, including any interest thereon, shall be
applied to pay the full face amount of Bankers' Acceptances on the respective
maturity dates thereof, and shall be returned by the Canadian Lender to the
Canadian Borrower only when, and to the extent that, the amount of such cash
held by the Canadian Lender exceeds the aggregate full face amount of all
outstanding Bankers' Acceptances at such time and no Default then exists. If the
Credit Obligations become or are declared immediately due and payable, the
Canadian Lender may apply such cash, including any interest thereon, to the
payment of any of the Credit Obligations as provided in Section 3.5.6 of the
Guarantee and Security Agreement.  In the event for any reason the Canadian
Borrower wishes to prepay an outstanding Bankers' Acceptance prior to its stated
maturity date, the Canadian Borrower must provide at least three Banking Days
prior written notice to the Canadian Lender and, at the time of such prepayment,
shall indemnify the Canadian Lender for any loss or expense (including loss of
profits and breakage costs) that the Canadian Lender may incur as a result of
such prepayment.

     4.6   Reborrowing; Application of Payments, etc.
           ------------------------------------------

          4.6.1   Reborrowing. The amounts of the Revolving Loan or the Canadian
                  ----------- 
     Loan prepaid pursuant to Section 4.3 may be reborrowed from time to time
     prior to the Final Maturity Date in accordance with Section 2.1 or Sections
     2.2 or 2.3, respectively, subject to the limits set forth therein.

          4.6.2   Order of Application.  Any prepayment of the Loan pursuant to
                  --------------------                                         
     Sections 4.2.2, 4.2.3, 4.2.4 or 4.2.5 shall be applied pro rata to the
     Revolving Loan (and to the permanent reduction of the Revolving Loan
     Commitments whether or not any portion of the Revolving Loan is then
     outstanding) and to the Canadian Loan (and to the permanent reduction of
     the Canadian Loan Commitments whether or not any portion of the Canadian
     Loan is then outstanding), based on the relative amounts of the Maximum
     Amount of Revolving Credit and the Maximum Amount of Canadian Credit. Any
     prepayment pursuant to Sections 4.2.2, 4.2.3, 4.2.4 or 4.2.5 allocated to
     the Revolving

                                      -50-
<PAGE>
 
     Loan shall be applied first pro rata to any Disproportionate Advances, with
     any balance to the other portion of the Revolving Loan. Subject to the
     foregoing, any prepayment of the Revolving Loan shall be applied first to
     the portion of the Revolving Loan not then subject to Eurodollar Pricing
     Options, then the balance of any such prepayment shall be applied to the
     portion of the Revolving Loan then subject to Eurodollar Pricing Options,
     in the chronological order of the respective maturities thereof (or as the
     U.S. Borrower may otherwise specify in writing), together with any payments
     required by Section 3.2.4. Subject to the foregoing, any prepayment of the
     Canadian Loan shall be applied first to the portion of the Canadian Loan
     consisting of revolving loans under Section 2.2, then the balance of any
     prepayment shall be applied to payment of Bankers' Acceptances, in the
     chronological order of the respective maturities thereof (or as the
     Canadian Borrower may otherwise specify in writing), together with any
     payments required by Section 4.5.

           4.6.3.   Payment Due.  Notice of prepayment having been given in
                    -----------                                            
     accordance with Section 4.3, and whether or not notice is given of
     prepayments pursuant to Section 4.2, the amount specified to be prepaid
     shall become due and payable on the date specified for prepayment.

           4.6.4.   Payments for Lenders.  All payments of the Revolving Loan
                    --------------------
     hereunder shall be made to the Agent for the account of the Lenders in
     accordance with the Lenders' respective Percentage Interests in the
     Revolving Loan. All payments of the Canadian Loan hereunder shall be made
     to the Canadian Lender for its own account.

     4.7.  Currency of Payments.  Any payment of principal of or interest on
           --------------------
any portion of the Credit Obligations shall be made in the currency in which
such portion of the Credit Obligations is denominated. All payments of fees
(including commitment fees), indemnities, expenses and other amounts owing
hereunder shall be made in United States Funds.

 5.  Conditions to Extending Credit.
     ------------------------------ 

     5.1.  Conditions on Initial Closing Date.  The obligations of the Lenders 
           ----------------------------------
to make the initial extension of credit pursuant to Section 2 shall be subject
to the satisfaction, on or before the Initial Closing Date, of the conditions
set forth in this Section 5.1 as well as the further conditions in Section 5.2.
If the conditions set forth in this Section 5.1 are not met on or prior to the
Initial Closing Date, the Lenders shall have no obligation to make any
extensions of credit hereunder.

           5.1.1.   Notes.  The U.S. Borrower shall have duly executed and
                    -----
     delivered to the Agent a Revolving Note for each Lender having a Commitment
     with respect thereto who has requested delivery of a Note prior to the
     Initial Closing Date, and the Canadian Borrower shall have duly executed
     and delivered a Canadian Note for the Canadian Lender if it has requested
     delivery of a Note prior to the Initial Closing Date.

                                      -51-
<PAGE>
 
           5.1.2.   Payment of Fees.  The Borrowers shall have paid to the Agent
                    ---------------
     and the Syndication Agent the fees contemplated by the separate agreement
     among the Agent, the Syndication Agent and the Company dated on or prior to
     the date hereof.

           5.1.3.   Legal Opinions.  The Lenders shall have received from the 
                    --------------
     following counsel their respective opinions with respect to the
     transactions contemplated by the Credit Documents, which opinions shall be
     in form and substance reasonably satisfactory to the Required Lenders:

           (a)   Perkins Coie, special counsel for the Company and its
     Washington Subsidiaries.

           (b)   Cherrington Minten & Easingwood, special counsel for the
     British Columbia, Canada Subsidiaries of the Company.

           (c)   Zalapski & Pahl, special counsel for the Alberta, Canada
     Subsidiaries of the Company.

           (d)   McMillan Binch, special counsel for the Ontario, Canada
     Subsidiary of the Company.

           (e)   Holland & Hart, special counsel for the Wyoming Subsidiaries
     of the Company.

           (f)   Gunster Yoakley, Valdes-Fauli & Stewart, P.A., special counsel
     for the Florida Subsidiary of the Company.

           (g)   Ropes & Gray, special counsel for the Agent.

           (h)   Borden & Elliott, special Canadian counsel for the Agent.

           The Company authorizes and directs its special counsel to furnish the
     foregoing opinions.

           5.1.4.   Guarantee and Security Agreement; Canadian Guarantee and
                    --------------------------------------------------------
     Security Documents. Each of the U.S. Borrower and the Guarantors which are
     ----------------------
     U.S. Subsidiaries shall have duly authorized, executed and delivered to the
     Agent a Guarantee and Security Agreement in substantially the form of
     Exhibit 5.1.4 (the "Guarantee and Security Agreement"), as well as any
                         --------------------------------
     patent and trademark security agreements and copyright security agreements
     contemplated therein. Each of the Canadian Borrower and the Guarantors
     which are Canadian Subsidiaries shall have duly authorized, executed and
     delivered to the Agent a Guarantee and a Debenture or Mortgage and Security
     Agreement appropriate for Canadian law in substance comparable to the
     Guarantee and Security

                                      -52-
<PAGE>
 
     Agreement and in form reasonably satisfactory to the Required Lenders
     (collectively, the "Canadian Guarantee and Security Documents").
                         -----------------------------------------

           5.1.5.   Real Estate Collateral.  The Obligors shall have duly
                    ----------------------                               
     authorized, executed, acknowledged and delivered to the Agent real property
     mortgages and leasehold mortgages (or Canadian debentures or mortgages) and
     other real estate documents to the extent required by Section 6.20.3, in
     each case in form and substance reasonably satisfactory to the Agent.

           5.1.6.   Perfection of Security.  Each Obligor shall have duly
                    ----------------------                               
     authorized, executed, acknowledged, delivered, filed, registered and
     recorded such security agreements, notices, financing statements and other
     instruments as the Agent may have reasonably requested in order to perfect
     the Liens purported or required pursuant to the Credit Documents to be
     created in the Credit Security and shall have paid all filing or recording
     fees or taxes required to be paid in connection therewith, including any
     recording, mortgage, documentary, transfer or intangible taxes.

           5.1.7.   Exercise of Warrants.  Warrants to purchase common stock
                    --------------------
     of the Company shall have been exercised for cash proceeds of at least
     $10,000,000, all of which shall have been invested as equity in the U.S.
     Borrower.

           5.1.8.   Solvency, etc.
                    ------------- 

           (a)   After giving effect to incurrence of the Credit Obligations,
     the Company and its Subsidiaries, taken as a whole:

                     (i)    will be solvent;

                     (ii)   will have assets having a fair saleable value in
           excess of the amount required to pay their probable liability on
           their existing debts as such debts become absolute and mature;

                     (iii)  will have access to adequate capital for the conduct
           of their business; and

                     (iv)   will have the ability to pay their debts from time
           to time incurred as such debts mature.

           (b)   Consolidated Adjusted EBITDA for the fiscal year ended February
     28, 1998 shall equal or exceed $3,500,000.

           (c)   Cash and Cash Equivalents of the Company and its Subsidiaries
     shall be less than $5,000,000.

                                      -53-
<PAGE>
 
           (d)   The Company shall have furnished to the Lenders a certificate,
     signed by a Financial Officer, to the effect that the closing conditions in
     Sections 5.1.7 and 5.1.8 have been satisfied.

           5.1.9.   Adverse Market Change.  Since April 9, 1998 no material
                    ---------------------
     adverse change shall have occurred in the syndication markets for credit
     facilities similar in nature to this Agreement and no material disruption
     of or material adverse change in the financial, banking or capital markets
     that would have an adverse effect on such syndication market shall have
     occurred, in each case as determined by the Agent and the Syndication Agent
     in their sole discretion.

           5.1.10.  Proper Proceedings.  This Agreement, each other Credit
                    ------------------
     Document and the transactions contemplated hereby and thereby shall have
     been authorized by all necessary corporate or other proceedings. All
     necessary consents, approvals and authorizations of any governmental or
     administrative agency or any other Person of any of the transactions
     contemplated hereby or by any other Credit Document shall have been
     obtained and shall be in full force and effect.

           5.1.11.  General.  All legal and corporate proceedings in connection
                    -------
     with the transactions contemplated by this Agreement shall be reasonably
     satisfactory in form and substance to the Agent and the Agent shall have
     received copies of all documents, including certified copies of the Charter
     and By-laws of the Company and the other Obligors, records of corporate
     proceedings, certificates as to signatures and incumbency of officers and
     opinions of counsel, which the Agent may have reasonably requested in
     connection therewith, such documents where appropriate to be certified by
     proper corporate or governmental authorities.

     5.2.  Conditions to Each Extension of Credit.  The obligations of the
           --------------------------------------                         
Lenders to make any extension of credit pursuant to Section 2 shall be subject
to the satisfaction, on or before the Closing Date for such extension of credit,
of the following conditions:

           5.2.1.   Officer's Certificate.  The representations and warranties
                    ---------------------
     contained in Section 7 shall be true and correct on and as of such Closing
     Date with the same force and effect as though made on and as of such date
     (except as to any representation or warranty which refers to a specific
     earlier date); no Default shall exist on such Closing Date prior to or
     immediately after giving effect to the requested extension of credit; no
     Material Adverse Change shall have occurred since February 28, 1998; and
     the U.S. Borrower or the Canadian Borrower, as the case may be, shall have
     furnished to the Agent and (in the case of the Canadian Loan) the Canadian
     Lender in connection with the requested extension of credit a certificate
     to these effects, in substantially the form of Exhibit 5.2.1, signed by a
     Financial Officer.

                                      -54-
<PAGE>
 
           5.2.2.   Legality, etc.  The making of the requested extension of
                    -------------
     credit shall not (a) subject any Lender to any penalty or special tax
     (other than a Tax for which the Borrower is required to reimburse the
     Lenders under Section 3.5) or (b) be prohibited by any Legal Requirement.

6.   General Covenants.  Each of the Company, each of the Borrowers and the
     -----------------                                                     
other Guarantors covenants that, until all of the Credit Obligations shall have
been paid in full and until the Lenders' commitments to extend credit under this
Agreement and any other Credit Document shall have been irrevocably terminated,
the Company and its Subsidiaries will comply with the following provisions:

     6.1.  Taxes and Other Charges; Accounts Payable.
           ----------------------------------------- 

           6.1.1.   Taxes and Other Charges.  Each of the Company and its
                    -----------------------                              
     Subsidiaries shall duly pay and discharge, or cause to be paid and
     discharged, before the same becomes in arrears, all taxes, assessments and
     other governmental charges imposed upon such Person and its properties,
     sales or activities, or upon the income or profits therefrom, as well as
     all claims for labor, materials or supplies which if unpaid might by law
     become a Lien upon any of its property; provided, however, that any such
                                             --------  -------
     tax, assessment, charge or claim need not be paid if the validity or amount
     thereof shall at the time be contested in good faith by appropriate
     proceedings and if such Person shall, in accordance with GAAP, have set
     aside on its books adequate reserves with respect thereto; and provided,
                                                                    --------
     further, that each of the Company and its Subsidiaries shall pay or bond,
     -------
     or cause to be paid or bonded, all such taxes, assessments, charges or
     other governmental claims immediately upon the entry of a judgment to
     foreclose any Lien which may have attached as security therefor (except to
     the extent such foreclosure has been dismissed or stayed).

           6.1.2.   Accounts Payable.  Each of the Company and its Subsidiaries
                    ----------------
     shall promptly pay when due, or in conformity with customary trade terms,
     all accounts payable incident to the operations of such Person not referred
     to in Section 6.1.1; provided, however, that any such accounts payable need
                          --------  -------
     not be paid if the validity or amount thereof shall at the time be
     contested in good faith and if such Person shall, in accordance with GAAP,
     have set aside on its books adequate reserves with respect thereto.

     6.2.  Conduct of Business, etc.
           ------------------------ 

           6.2.1.   Types of Business.  The Company and its Subsidiaries shall
                    -----------------                                         
     engage only in the business of (a) designing, engineering, constructing,
     owning, operating and maintaining Towers (including rooftop Towers) for its
     own account and for third parties, acquiring Towers and Tower Companies,
     leasing space on such Towers to tenants, managing the construction of,
     ownership of and leasing of space on Towers for third

                                      -55-
<PAGE>
 
     parties, and providing site administration and development services to
     wireless telecommunications and broadcast companies and (b) other
     activities related thereto.

           6.2.2.   Maintenance of Properties.  Each of the Company and its
                    -------------------------                              
     Subsidiaries:

           (a)   shall keep its properties in such repair, working order and
     condition, and shall from time to time make such repairs, replacements,
     additions and improvements thereto, as are necessary for the efficient
     operation of its businesses and shall comply at all times in all material
     respects with all material franchises, licenses and leases to which it is
     party so as to prevent any loss or forfeiture thereof or thereunder, except
     where (i) compliance is at the time being contested in good faith by
     appropriate proceedings and (ii) failure to comply with the provisions
     being contested has not resulted, and does not create a material risk of
     resulting, in the aggregate in any Material Adverse Change; and

           (b)   shall do all things necessary to preserve, renew and keep in
     full force and effect and in good standing its legal existence and
     authority necessary to continue its business; provided, however, that this
                                                   --------  -------           
     Section 6.2.2(b) shall not prevent the merger, consolidation or liquidation
     of Subsidiaries permitted by Section 6.11.

           6.2.3.   Statutory Compliance.  Each of the Company and its
                    --------------------
     Subsidiaries shall comply in all material respects with all valid Legal
     Requirements applicable to it, except where (a) compliance therewith shall
     at the time be contested in good faith by appropriate proceedings and (b)
     failure so to comply with the provisions being contested has not resulted,
     and does not create a material risk of resulting, in the aggregate in any
     Material Adverse Change.

           6.2.4.   Compliance with Material Agreements.  Each of the Company
                    -----------------------------------
     and its Subsidiaries shall comply in all material respects with the
     Material Agreements (to the extent not in violation of the other provisions
     of this Agreement or any other Credit Document). Without the prior written
     consent of the Required Lenders, no Material Agreement shall be amended,
     modified, waived or terminated in any manner that would have a material
     adverse effect on the interests of the Lenders.

     6.3.  Insurance.
           --------- 

           6.3.1.   Business Interruption Insurance.  Each of the Company and
                    -------------------------------
     its Subsidiaries shall maintain with financially sound and reputable
     insurers insurance related to interruption of business, either for loss of
     revenues or for extra expense, in the manner customary for businesses of
     similar size engaged in similar activities.

           6.3.2.   Property Insurance.  Each of the Company and its
                    ------------------
     Subsidiaries shall keep its assets which are of an insurable character
     insured by financially sound and reputable insurers against theft and fraud
     and against loss or damage by fire, explosion

                                      -56-
<PAGE>
 
     and hazards insured against by extended coverage to the extent, in amounts
     and with deductibles at least as favorable as those generally maintained by
     businesses of similar size engaged in similar activities.

           6.3.3.   Liability Insurance.  Each of the Company and its
                    -------------------
     Subsidiaries shall maintain with financially sound and reputable insurers
     insurance against liability for hazards, risks and liability to persons and
     property, including product liability insurance, to the extent, in amounts
     and with deductibles at least as favorable as those generally maintained by
     businesses of similar size engaged in similar activities; provided,
     however, that it may effect workers' compensation insurance or similar
     coverage with respect to operations in any particular state or other
     jurisdiction through an insurance fund operated by such state or
     jurisdiction or by meeting the self-insurance requirements of such state or
     jurisdiction.

           6.3.4.   Key Executive Life Insurance.  The Company shall maintain
                    ----------------------------
     with financially sound and reputable insurers life insurance policies on
     each of Calvin J. Payne and S. Roy Jeffrey in an amount of at least
     $1,000,000 in form reasonably satisfactory to the Agent.

           6.3.5.   Flood Insurance.  Each of the Company and its Subsidiaries
                    ---------------
     shall at all times keep each parcel of real property owned or leased by it
     which is (a) included in the Credit Security, (b) in an area determined by
     the Director of the Federal Emergency Management Agency to be subject to
     special flood hazard and (c) in a community participating in the National
     Flood Insurance Program, insured against such special flood hazards in an
     amount necessary to ensure compliance with the federal National Flood
     Insurance Act of 1968.

     6.4.  Financial Statements and Reports.  Each of the Company and its
           --------------------------------                              
Subsidiaries shall maintain a system of accounting in which correct entries
shall be made of all transactions in relation to their business and affairs in
accordance with generally accepted accounting practice. The fiscal year of the
Company and its Subsidiaries shall end on February 28 in each year and the
fiscal quarters of the Company and its Subsidiaries shall end on May 31, August
31, November 30 and February 28 in each year.

           6.4.1.   Annual Reports.  The Company shall furnish to the Lenders as
                    --------------                                              
     soon as available, and in any event within 120 days after the end of each
     fiscal year, the Consolidated and Consolidating balance sheets of the
     Company and its Subsidiaries as at the end of such fiscal year, the
     Consolidated and Consolidating statements of income and Consolidated
     statements of changes in shareholders' equity and of cash flows of the
     Company and its Subsidiaries for such fiscal year (all in reasonable
     detail) and, in the case of Consolidated financial statements, comparative
     figures for the immediately preceding fiscal year, all accompanied by:

                                      -57-
<PAGE>
 
           (a)   Reports of Moss Adams LLP (or, if they cease to be auditors of
     the Company and its Subsidiaries, independent certified public accountants
     of recognized national standing reasonably satisfactory to the Required
     Lenders), containing no material qualification, to the effect that they
     have audited the foregoing Consolidated financial statements in accordance
     with generally accepted auditing standards and that such Consolidated
     financial statements present fairly, in all material respects, the
     financial position of the Company and its Subsidiaries covered thereby at
     the dates thereof and the results of their operations for the periods
     covered thereby in conformity with GAAP.

           (b)   The statement of such accountants that they have caused this
     Agreement to be reviewed and that in the course of their audit of the
     Company and its Subsidiaries no facts have come to their attention that
     cause them to believe that any Default exists and in particular that they
     have no knowledge of any Default under the Computation Covenants or, if
     such is not the case, specifying such Default and the nature thereof.  This
     statement is furnished by such accountants with the understanding that the
     examination of such accountants cannot be relied upon to give such
     accountants knowledge of any such Default except as it relates to
     accounting or auditing matters within the scope of their audit.

           (c)   A certificate of the Company signed by a Financial Officer to
     the effect that such officer has caused this Agreement to be reviewed and
     has no knowledge of any Default, or if such officer has such knowledge,
     specifying such Default and the nature thereof, and what action the Company
     has taken, is taking or proposes to take with respect thereto.

           (d)   Computations by the Company comparing the financial statements
     referred to above with the most recent budget for such fiscal year
     furnished to the Lenders in accordance with Section 6.4.5.

           (e)   Computations by the Company in substantially the form of
     Exhibit 6.4 demonstrating, as of the end of such fiscal year, compliance
     with the Computation Covenants, signed by a Financial Officer.

           (f)   Calculations, as at the end of such fiscal year, of (i) the
     Accumulated Benefit Obligations for each Plan (other than Multiemployer
     Plans) and (ii) the fair market value of the assets of such Plan allocable
     to such benefits.

           (g)   A schedule, certified by a Financial Officer, showing as of the
     end of such fiscal year (i) the location of all Towers, the ownership of
     the real property on which each Tower is located, which Towers are capable
     of being moved from their present location, and the contribution by each
     Tower to Consolidated Tower Revenues as then estimated in good faith by the
     Company and (ii) an open bid summary report and a site development backlog
     report.

                                      -58-
<PAGE>
 
           (h)   Supplements to Exhibits 7.1, 7.3, 7.14 and 7.15 showing any
     changes in the information set forth in such exhibits not previously
     furnished to the Lenders in writing, as well as any changes in the Charter,
     By-laws or incumbency of officers of the Obligors from those previously
     certified to the Agent.

           (i)   In the event of a change in GAAP after February 28, 1998,
     computations by the Company, signed by a Financial Officer, reconciling the
     financial statements referred to above with financial statements prepared
     in accordance with GAAP as applied to the other covenants in Section 6 and
     related definitions.

           (j)   In reasonable detail, management's discussion and analysis of
     the results of operations and the financial condition of the Company and
     its Subsidiaries as at the end of and for the year covered by such
     financial statements.

           6.4.2.   Quarterly Reports.  The Company shall furnish to the Lenders
                    -----------------
     as soon as available and, in any event, within 45 days after the end of
     each of the first three fiscal quarters of the Company, the internally
     prepared Consolidated and Consolidating balance sheet of the Company and
     its Subsidiaries as of the end of such fiscal quarter, the Consolidated and
     Consolidating statements of income, of changes in shareholders' equity and
     of cash flows of the Company and its Subsidiaries for such fiscal quarter
     and for the portion of the fiscal year then ended (all in reasonable
     detail) and comparative figures for the same period in the preceding fiscal
     year, all accompanied by:

           (a)   A certificate of the Company signed by a Financial Officer to
     the effect that such financial statements have been prepared in accordance
     with GAAP and present fairly, in all material respects, the financial
     position of the Company and its Subsidiaries covered thereby at the dates
     thereof and the results of their operations for the periods covered
     thereby, subject only to normal year-end audit adjustments and the addition
     of footnotes.

           (b)   A certificate of the Company signed by a Financial Officer to
     the effect that such officer has caused this Agreement to be reviewed and
     has no knowledge of any Default, or if such officer has such knowledge,
     specifying such Default and the nature thereof and what action the Company
     has taken, is taking or proposes to take with respect thereto.

           (c)   Computations by the Company comparing the financial statements
     referred to above with the most recent budget for the period covered
     thereby furnished to the Lenders in accordance with Section 6.4.5.

                                      -59-
<PAGE>
 
           (d)   Computations by the Company in substantially the form of
     Exhibit 6.4 demonstrating, as of the end of such quarter, compliance with
     the Computation Covenants, signed by a Financial Officer.

           (e)   A schedule, certified by a Financial Officer, showing as of
     the end of such fiscal quarter (i) the location of all Towers, which Towers
     are capable of being moved from their present location, the ownership of
     the real property on which each Tower is located and the contribution by
     each Tower to Consolidated Tower Revenues as then estimated in good faith
     by the Company and (ii)  an open bid summary report and a site development
     backlog report.

           (f)   Supplements to Exhibits 7.1, 7.3, 7.14 and 7.15 showing any
     changes in the information set forth in such exhibits not previously
     furnished to the Lenders in writing, as well as any changes in the Charter,
     Bylaws or incumbency of officers of the Obligors from those previously
     certified to the Agent.

           (g)   In reasonable detail, management's discussion and analysis of
     the results of operations and financial condition of the Company and its
     Subsidiaries as at the end of and for the fiscal period covered by the
     financial statements referred to above.

           6.4.3.   Currency Exchange Report; Compliance.  The Company shall
                    ------------------------------------
     furnish to the Lenders as soon as available and, in any event, within 25
     days after the end of each month, a report containing a calculation of the
     Canadian Loan in the Equivalent Amount of United States Funds based on the
     foreign currency exchange rates as of the end of such month and, in the
     event the amount of the Canadian Loan as calculated above is at least 5%
     larger or smaller than the amount of the Canadian Loan as calculated for
     purposes of the most recent computations of the Computation Covenants, new
     computations by the Company in substantially the form of Exhibit 6.4
     demonstrating, as of the end of the most recently completed fiscal quarter,
     compliance with the Computation Covenants with the Canadian Loan as
     calculated above, signed by a Financial Officer.

           6.4.4.   Tower Acquisition Reports.  The Company will deliver to the
                    -------------------------                                  
     Agent 15 Banking Days' prior written notice of the proposed acquisition of
     any new Towers (including real property sites for Towers) for a proposed
     cost that equals or exceeds $2,500,000 for any acquisition or series of
     related acquisitions and the proposed cost and projected revenue thereof
     (whether or not the costs of such acquisition are to be funded by the
     Company from its own sources or from the proceeds of the Loan). Such notice
     shall specify a description and the locations of the new Towers (including
     Towers owned by Tower Companies), the name and address of the owner or
     lessee, as appropriate, of the real property on which they are located,
     and, a memorandum summarizing the results of the due diligence review of
     such acquisition or series of related acquisitions and such other documents
     or information owned or within the control of the Company and its
     Subsidiaries as the Required Lenders may reasonably require.

                                      -60-
<PAGE>
 
           6.4.5.  Other Reports.  The Company shall promptly furnish to the
                   -------------                                            
     Lenders:

           (a)   As soon as prepared and in any event before the beginning of
     each fiscal year, an annual budget and operating projections for such
     fiscal year of the Company and its Subsidiaries, prepared in a manner
     consistent with the manner in which the financial projections described in
     Section 7.2.1 were prepared and showing, in any event, projected net
     income, cash flows and the Capital Expenditures budget.

           (b)   Any material updates of such budget and projections.

           (c)   Any management letters furnished to the Company or any of its
     Subsidiaries by the Company's auditors.

           (d)   All budgets, projections, statements of operations and other
     reports furnished generally to the shareholders of the Company.

           (e)   Such registration statements, proxy statements and reports,
     including Forms S-1, S-2, S-3, S-4, 10-K, 10-Q and 8-K, as may be filed by
     the Company or any of its Subsidiaries with the Securities and Exchange
     Commission.

           (f)   Any 90-day letter or 30-day letter from the federal Internal
     Revenue Service (or the equivalent notice received from state or other
     taxing authorities) asserting tax deficiencies against the Company or any
     of its Subsidiaries.

           6.4.6.  Notice of Litigation, Defaults, etc. The Company shall
                   -----------------------------------
     promptly furnish to the Lenders notice of any litigation or any
     administrative or arbitration proceeding (a) which creates a material risk
     of resulting, after giving effect to any applicable insurance, in the
     payment by the Company and its Subsidiaries of more than $500,000 or (b)
     which results, or creates a material risk of resulting, in a Material
     Adverse Change. Promptly upon acquiring knowledge thereof, the Company
     shall notify the Lenders of the existence of any Default or Material
     Adverse Change, specifying the nature thereof and what action the Company
     or any of its Subsidiaries has taken, is taking or proposes to take with
     respect thereto.

           6.4.7.  ERISA Reports. The Company shall furnish to the Lenders as
                   -------------
     soon as available the following items with respect to any Plan:

           (a)   any request for a waiver of the funding standards or an
     extension of the amortization period,

           (b)   notice of any reportable event (as defined in section 4043 of
     ERISA), unless the notice requirement with respect thereto has been waived
     by regulation,

                                      -61-
<PAGE>
 
           (c)   any notice received by any ERISA Group Person that the PBGC has
     instituted or intends to institute proceedings to terminate any Plan, or
     that any Multiemployer Plan is insolvent or in reorganization,

           (d)   notice of the possibility of the termination of any Plan by its
     administrator pursuant to section 4041 of ERISA, and

           (e)   notice of the intention of any ERISA Group Person to withdraw,
     in whole or in part, from any Multiemployer Plan.

           6.4.8.  Other Information; Audit.  From time to time at reasonable
                   ------------------------                                  
     intervals upon request of any authorized officer of any Lender, each of the
     Company and its Subsidiaries shall furnish to such Lender such other
     information regarding the business, assets, financial condition, income or
     prospects of the Company and its Subsidiaries as such officer may
     reasonably request, including copies of all tax returns, licenses,
     agreements, leases and instruments to which any of the Company or its
     Subsidiaries is party. Each Lender's authorized officers and
     representatives shall have the right during normal business hours upon
     reasonable notice and at reasonable intervals to examine the books and
     records of the Company and its Subsidiaries, to make copies and notes
     therefrom for the purpose of ascertaining compliance with or obtaining
     enforcement of this Agreement or any other Credit Document. The Agent, upon
     reasonable advance notice, may undertake to have the Company and its
     Subsidiaries reviewed by the Agent's commercial financial examiners and
     fixed asset appraisers.

     6.5.  Certain Financial Tests.
           ----------------------- 

           6.5.1.  Consolidated Total Debt to Consolidated Adjusted EBITDA.
                   ------------------------------------------------------- 
     Consolidated Total Debt shall not on any date exceed the percentage set
     forth in the table below of Consolidated Adjusted EBITDA for the most
     recently completed period of four consecutive fiscal quarters for which
     financial reports have been (or are required to have been) furnished to the
     Lenders in accordance with Section 6.4.1 or 6.4.2.

                   Period Ending              Percentage
                   -------------              ----------

           Prior to May 31, 2000              600%

           June 1, 2000 through               550%
              May 31, 2001

           June 1, 2001 through               500%
              May 31, 2002
 

                                      -62-
<PAGE>
 
           June 1, 2002 through                    450%
              May 31, 2003

           June 1, 2003 and thereafter             400%

           6.5.2.  Consolidated Senior Debt to Consolidated Adjusted EBITDA.
                   -------------------------------------------------------- 
     Consolidated Senior Debt shall not on any date exceed the percentage set
     forth in the table below of Consolidated Adjusted EBITDA for the most
     recently completed period of four consecutive fiscal quarters for which
     financial reports have been (or are required to have been) furnished to the
     Lenders in accordance with Section 6.4.1 or 6.4.2.

                    Period Ending               Percentage
                    -------------               ----------

           Prior to May 31, 2000                   500%

           June 1, 2000 through May 31, 2001       450%

           June 1, 2001 through May 31, 2002       400%

           June 1, 2002 through May 31, 2003       350%

           June 1, 2003 and thereafter             300%

           6.5.3.  Consolidated EBITDA to Consolidated Interest Expense. For
                   ----------------------------------------------------   
     each period of four consecutive fiscal quarters of the Company,
     Consolidated EBITDA shall equal or exceed the percentage set forth in the
     table below of Consolidated Interest Expense.

                    Period Ending          Percentage
                    -------------          ----------

           Prior to May 31, 2000              200%

           June 1, 2000 and thereafter        250%

           6.5.4.  Consolidated EBITDA to Consolidated Fixed Charges.  For each
                   -------------------------------------------------           
     period of four consecutive fiscal quarters of the Company, Consolidated
     EBITDA shall equal or exceed 110% of Consolidated Fixed Charges.

           6.5.5.  Consolidated Adjusted EBITDA.  For each period of four
                   ----------------------------                          
     consecutive fiscal quarters of the Company, Consolidated Adjusted EBITDA
     shall equal or exceed the sum of (a) $3,500,000 plus (b) 85% of
                                                     ----
     Consolidated Adjusted EBITDA properly allocable to Towers acquired or
     constructed for the account of the Company or any of its

                                      -63-
<PAGE>
 
     Subsidiaries after March 1, 1998 plus (c) 50% of Consolidated Adjusted
                                      ----
     EBITDA (only if a positive number) properly allocable to Subsidiaries or
     divisions acquired after March 1, 1998 that construct Towers for third
     parties.

          6.5.6.   Consolidated Net Worth. Consolidated Net Worth shall not at
                   ---------------------- 
     any time be less than the sum of (a) $12,000,000 plus (b) the Available
                                                      ----
     Fund.

          6.5.7.   Capital Expenditures.  Capital Expenditures with respect to
                   --------------------                                       
     Towers to be constructed or for which construction is not yet complete and
     owned by (or to be owned by) the Company and its Subsidiaries shall not
     exceed $5,000,000 in the aggregate at any one time outstanding; provided,
                                                                     --------
     however, that in no event shall this limitation apply to Capital
     -------
     Expenditures with respect to repairing, replacing or maintaining Towers
     following their completion or which are acquired with all construction
     complete.

     6.6  Indebtedness.  Neither the Company nor any of its Subsidiaries shall
          ------------                                                        
create, incur, assume or otherwise become or remain liable with respect to any
Indebtedness (or become contractually committed to do so), except the following:

          6.6.1.  Indebtedness in respect of the Credit Obligations.

          6.6.2.  Guarantees permitted by Section 6.7.

          6.6.3.  Current liabilities, other than Financing Debt, incurred in
     the ordinary course of business.

          6.6.4.  To the extent that payment thereof shall not at the time be
     required by Section 6.1, Indebtedness in respect of taxes, assessments,
     governmental charges and claims for labor, materials and supplies.

          6.6.5.  Indebtedness secured by Liens of carriers, warehouses,
     mechanics, landlords and other Persons permitted by Sections 6.8.5 and
     6.8.6.

          6.6.6.  Indebtedness in respect of judgments or awards (a) which have
     been in force for less than the applicable appeal period or (b) in respect
     of which the Company or any Subsidiary shall at the time in good faith be
     prosecuting an appeal or proceedings for review and, in the case of each of
     clauses (a) and (b), the Company or such Subsidiary shall have taken
     appropriate reserves therefor in accordance with GAAP and execution of such
     judgment or award shall not be levied.

          6.6.7.  To the extent permitted by Section 6.8.7, Indebtedness in
     respect of Capitalized Lease Obligations or secured by purchase money
     security interests; provided, however, that the aggregate principal amount
                         --------  -------                                     
     of all Indebtedness under this Section 6.6.7 

                                      -64-
<PAGE>
 
     plus Indebtedness under Sections 6.6.8 and 6.6.14 at any one time
     ----  
     outstanding shall not exceed $2,500,000.

           6.6.8.  Unsecured Indebtedness of the Company owing to sellers of
     Towers and Tower Companies so long as either (a) such Indebtedness is
     subordinated to the Credit Obligations on substantially the terms of
     Exhibit 6.6.8 and the aggregate principal amount of all Indebtedness under
     this clause (a) plus Indebtedness under Sections 6.6.7 and 6.6.14 at any
                     ----                                                    
     one time outstanding shall not exceed $2,500,000 or (b) the aggregate
     principal amount of Indebtedness owing to such sellers is covered by
     Letters of Credit.

           6.6.9.  Indebtedness in respect of deferred taxes arising in the
     ordinary course of business.

           6.6.10. Indebtedness in respect of inter-company loans and advances
     among the Company and its Subsidiaries which are not prohibited by Section
     6.9.

           6.6.11. Senior Subordinated Debt.

           6.6.12. Unfunded pension liabilities and obligations with respect to
     Plans so long as the Company and all other ERISA Group Persons are in
     compliance with Section 6.16.

           6.6.13. Other Indebtedness outstanding on the date hereof and
     described in Exhibit 7.3 and all renewals and extensions thereof not in
     excess of the amount thereof outstanding immediately prior to such renewal
     or extension or having a shorter average life or earlier maturity.

           6.6.14. Indebtedness (other than Financing Debt) in addition to the
     foregoing; provided, however, that the aggregate amount of all such
                --------  -------                                       
     Indebtedness under this Section 6.6.14 plus Indebtedness under Sections
                                            ----                            
     6.6.7 and 6.6.8 at any one time outstanding shall not exceed $2,500,000.

           6.6.15. Interest Rate Protection Agreements.

     6.7   Guarantees; Letters of Credit.  Neither the Company nor any of its
           -----------------------------                                     
Subsidiaries shall become or remain liable with respect to any Guarantee,
including reimbursement obligations, whether contingent or matured, under
letters of credit or other financial guarantees by third parties (or become
contractually committed do to so), except the following:

           6.7.1.  Letters of Credit and Guarantees of the Credit Obligations.

           6.7.2.  Guarantees by the Company of Indebtedness and other
     obligations incurred by its Subsidiaries and permitted by Section 6.6.

                                      -65-
<PAGE>
 
           6.7.3.  Senior Subordinated Notes.

     6.8.  Liens.  Neither the Company nor any of its Subsidiaries shall create,
           -----                                                                
incur or enter into, or suffer to be created or incurred or to exist, any Lien
(or become contractually committed to do so), except the following:

           6.8.1.  Liens on the Credit Security that secure the Credit
     Obligations.

           6.8.2.  Liens to secure taxes, assessments and other governmental
     charges, to the extent that payment thereof shall not at the time be
     required by Section 6.1.

           6.8.3.  Deposits or pledges made (a) in connection with, or to secure
     payment of, workers' compensation, unemployment insurance, old age pensions
     or other social security, (b) in connection with casualty insurance
     maintained in accordance with Section 6.3, (c) to secure the performance of
     bids, tenders, contracts (other than contracts relating to Financing Debt)
     or leases, (d) to secure statutory obligations or surety or appeal bonds,
     (e) to secure indemnity, performance or other similar bonds in the ordinary
     course of business or (f) in connection with contested amounts to the
     extent that payment thereof shall not at that time be required by Section
     6.1.

           6.8.4.  Liens in respect of judgments or awards, to the extent that
     such judgments or awards are permitted by Section 6.6.6 but only to the
     extent that such Liens are junior to the Liens on the Credit Security
     granted to secure the Credit Obligations.

           6.8.5.  Liens of carriers, warehouses, mechanics and similar Liens,
     in each case (a) in existence less than 90 days from the date of creation
     thereof or (b) being contested in good faith by the Company or any
     Subsidiary in appropriate proceedings (so long as the Company or such
     Subsidiary shall, in accordance with GAAP, have set aside on its books
     adequate reserves with respect thereto).

           6.8.6.  Encumbrances in the nature of (a) zoning restrictions, (b)
     easements, (c) restrictions of record on the use of real property, (d)
     landlords' and lessors' Liens on rented premises and (e) restrictions on
     transfers or assignment of leases, which in each case do not materially
     detract from the value of the encumbered property or impair the use thereof
     in the business of the Company or any Subsidiary.

           6.8.7.  Liens constituting (a) purchase money security interests
     (including mortgages, conditional sales, Capitalized Leases and any other
     title retention or deferred purchase devices) in real property, interests
     in leases or tangible personal property (other than inventory) existing or
     created on the date on which such property is acquired or within 60 days
     thereafter, and (b) the renewal, extension or refunding of any security
     interest referred to in the foregoing clause (a) in an amount not to exceed
     the amount 

                                      -66-
<PAGE>
 
     thereof remaining unpaid immediately prior to such renewal, extension or
     refunding; provided, however, that (i) each such security interest shall
                --------  -------
     attach solely to the particular item of property so acquired, and the
     principal amount of Indebtedness (including Indebtedness in respect of
     Capitalized Lease Obligations) secured thereby shall not exceed the cost
     (including all such Indebtedness secured thereby, whether or not assumed)
     of such item of property; and (ii) the aggregate principal amount of all
     Indebtedness secured by Liens permitted by this Section 6.8.7 shall not
     exceed the amount permitted by Section 6.6.7.

           6.8.8.  Restrictions under federal, provincial and state securities
     laws on the transfer of securities.

           6.8.9.  The sale of doubtful accounts receivable for collection in
     the ordinary course of business.

           6.8.10  Liens as in effect on the date hereof described in Exhibit
     7.3 (and renewals and replacements thereof) and securing Indebtedness
     permitted by Section 6.6.13.

           6.8.11. Depositary's liens, rights of set-off or similar rights and
     remedies as to deposit accounts.

     6.9.  Investments and Acquisitions.  Neither the Company nor any of its
           ----------------------------                                     
Subsidiaries shall have outstanding, acquire or hold any Investment (including
any Investment consisting of the acquisition of any business) (or become
contractually committed to do so), except the following:

           6.9.1.  Investments of the Company and its Subsidiaries in (a) Wholly
     Owned Subsidiaries which are Guarantors or Borrowers as of the date hereof
     or (b) Persons that have become Wholly Owned Subsidiaries and Guarantors
     after the date hereof in accordance with Section 6.9.5; provided, however,
                                                             --------  ------- 
     that no such Investment shall involve the transfer by the Company or the
     Borrowers of any material assets other than cash.

           6.9.2.  Intercompany loans and advances from any Wholly Owned
     Subsidiary to either of the Borrowers but in each case only to the extent
     reasonably necessary for Consolidated tax planning and working capital
     management.

           6.9.3.  Investments in Cash Equivalents.

           6.9.4.  Guarantees permitted by Section 6.7.

           6.9.5.  So long as immediately before and after giving effect thereto
     no Default exists, Investments of the Company and its Wholly Owned
     Subsidiaries consisting of the

                                      -67-
<PAGE>
 
     acquisition of Towers and at least 80% of the equity of Tower Companies;
     provided, however, that:
     --------  -------       

           (a)   at least 10 Banking Days, in the case of acquisitions or series
     of related acquisitions with a cost to the Company and its Subsidiaries
     equal to or exceeding $2,500,000, prior to any such acquisition, the
     Lenders shall receive computations provided by a Financial Officer
     demonstrating pro forma compliance with the Computation Covenants after
     giving effect to such acquisition and the materials required by Section
     6.4.4,

           (b)   the Company shall take all necessary action to cause any such
     newly acquired Tower Company to become a Guarantor and to perfect the
     Lenders' security interests in the newly acquired Towers and Designated
     Real Properties to the extent necessary to comply with Section 6.20.3,

           (c)   no more than 25% of the Tower Revenues anticipated to be
     derived from such acquired Towers or Tower Companies shall derive from PCS
     C-Block Providers, and

           (d)   in the case of any acquisition (or series of related
     acquisitions) involving consideration equal to or exceeding $5,000,000 by
     the Company and its Subsidiaries, the Lenders holding at least a majority
     of the Percentage Interests shall have provided their prior written
     consent.

     6.10. Distributions.  Neither the Company nor any of its Subsidiaries shall
           -------------                                                        
make any Distribution (or become contractually committed to do so), except the
following:

           6.10.1. So long as immediately before and after giving effect thereto
     no Default exists, Subsidiaries of the Company may make Distributions to
     the Company or any Wholly Owned Subsidiary of the Company and the Company
     and its Subsidiaries may make Investments permitted by Sections 6.9.1 and
     6.9.2.

           6.10.2.  To the extent permitted by the applicable subordination
     terms, the Company may make regularly scheduled, mandatory payments of
     interest on and principal of the subordinated Indebtedness permitted by
     Sections 6.6.8 and 6.6.11.

           6.10.3.  So long as immediate before and after giving effect thereto
     no Default exists, the Company may make Distributions up to $200,000 per
     year to repurchase Company stock and options to acquire such stock owned by
     employees whose employment with the Company and its Subsidiaries has then
     terminated.

     6.11. Asset Dispositions and Mergers.  Neither the Company nor any of its
           ------------------------------                                     
Subsidiaries shall merge or enter into a consolidation or sell, lease, exchange,
sell and lease back, 

                                      -68-
<PAGE>
 
sublease or otherwise dispose of any of its assets (or become contractually
committed to do so), except the following:

           6.11.1.  The Company and any of its Subsidiaries may sell or
     otherwise dispose of (a) inventory and Cash Equivalents in the ordinary
     course of business and (b) tangible assets to be replaced in the ordinary
     course of business within 12 months by other tangible assets of equal or
     greater value or (c) tangible assets (other than Towers) that are no longer
     used or useful in the business of the Company or such Subsidiary; provided,
                                                                       --------
     however, that the fair value of all assets sold or disposed of pursuant to
     -------
     this clause (c) shall not be material.

           6.11.2. Dispositions of immaterial assets outside the ordinary course
     of business; provided, however, that the fair value of all assets sold or
                  --------  -------                                           
     disposed of pursuant to this Section 6.11.2 after the date hereof shall not
     exceed $1,000,000 in the aggregate.

           6.11.3. Any Wholly Owned Subsidiary of the Company (other than either
     of the Borrowers) may merge, consolidate or be liquidated into either of
     the Borrowers or any other Wholly Owned Subsidiary of either of the
     Borrowers so long as after giving effect to any such merger to which such
     Borrower is a party such Borrower shall be the surviving or resulting
     Person.

           6.11.4. Mergers constituting Investments permitted by Section 6.9.5.

           6.11.5. Licensing of and leasing of Tower space and intangible assets
     for fair value in the ordinary course of business.

           6.11.6. So long as immediately before and after giving effect thereto
     no Default exists, transfers for fair value to any Person who sells or
     leases a Tower or Tower Company to the Company or one of its Subsidiaries
     of such portions of the real property on which the applicable Towers are
     located as are not necessary for the operation of the Towers.

           6.11.7. So long as the Net Asset Sale Proceeds thereof are applied to
     repay the Loan as required by Section 4.3.3 and so long as immediately
     before and after giving effect thereto no Default exists, the Company and
     its Subsidiaries may sell for fair value during any year Towers
     contributing not more than 5% of Consolidated Tower Revenues for the
     Company's most recently completed fiscal year; provided, however, that the
                                                    --------  -------          
     sum of the foregoing percentages of Consolidated Tower Revenues for all
     Towers sold pursuant to this Section 6.11.6 since the date hereof shall not
     exceed 15%.

           6.11.8. So long as immediately before and after giving effect thereto
     no Default exists, the Company and its Subsidiaries may enter into sale and
     leaseback 

                                      -69-
<PAGE>
 
     transactions with respect to the real property upon which the Towers are
     located (but not with respect to the Towers themselves) in an aggregate
     amount not to exceed $200,000.

     6.12.  Issuance of Stock by Subsidiaries; Subsidiary Distributions.
            ----------------------------------------------------------- 

            6.12.1. Issuance of Stock by Subsidiaries. No Subsidiary of the
                    ---------------------------------
     Company shall issue or sell any shares of its capital stock or other
     evidence of beneficial ownership to any Person other than (a) the Company
     or any Wholly Owned Subsidiary of the Company, which shares shall have been
     pledged to the Agent as part of the Credit Security to the extent required
     by the Guarantee and Security Agreement and (b) directors of Subsidiaries
     as qualifying shares to the extent required by Legal Requirements and, in
     the case of Foreign Subsidiaries, shares required by Legal Requirements to
     be held by foreign nationals.

            6.12.2. No Restrictions on Subsidiary Distributions. Except for this
                    -------------------------------------------   
     Agreement, the Credit Documents and the Senior Subordinated Notes Purchase
     Agreement, neither the Company nor any Subsidiary shall enter into or be
     bound by any agreement (including covenants requiring the maintenance of
     specified amounts of net worth or working capital) restricting the right of
     any Subsidiary to make Distributions or extensions of credit to the
     Borrowers (directly or indirectly through another Subsidiary).

     6.13.  Voluntary Prepayments of Other Indebtedness. Neither the Company nor
            -------------------------------------------  
any of its Subsidiaries shall make any voluntary prepayment of principal of or
interest on any Financing Debt (other than the Credit Obligations) or make any
voluntary redemptions or repurchases of Financing Debt (other than the Credit
Obligations), in each case except in order to facilitate a refinancing of
Indebtedness permitted by Section 6.6.

     6.14.  Derivative Contracts.  Neither the Company nor any of its
            --------------------                                     
Subsidiaries shall enter into any Interest Rate Protection Agreement, foreign
currency exchange contract or other financial or commodity derivative contracts
except to provide hedge protection for an underlying economic transaction in the
ordinary course of business.

     6.15.  Negative Pledge Clauses.  Neither the Company nor any of its
            -----------------------                                     
Subsidiaries shall enter into any agreement, instrument, deed or lease which
prohibits or limits the ability of the Company or any of its Subsidiaries to
create, incur, assume or suffer to exist any Lien upon any of their respective
properties, assets or revenues, whether now owned or hereafter acquired, or
which requires the grant of any collateral for such obligation if collateral is
granted for another obligation, except the following:

            6.15.1.  This Agreement and the other Credit Documents.

            6.15.2.  Covenants in documents creating Liens permitted by Section
     6.8 prohibiting further Liens on the assets encumbered thereby.

           

                                      -70-
<PAGE>
 
               6.15.3.  The Senior Subordinated Notes Purchase Agreement.

     6.16.     ERISA, etc.  Each of the Company and its Subsidiaries shall 
               ----------                                                  
comply, and shall cause all ERISA Group Persons to comply, in all material
respects, with the provisions of ERISA and the Code applicable to each Plan.
Each of the Company and its Subsidiaries shall meet, and shall cause all ERISA
Group Persons to meet, all minimum funding requirements applicable to them with
respect to any Plan pursuant to section 302 of ERISA or section 412 of the Code,
without giving effect to any waivers of such requirements or extensions of the
related amortization periods which may be granted. At no time shall the
Accumulated Benefit Obligations under any Plan that is not a Multiemployer Plan
exceed the fair market value of the assets of such Plan allocable to such
benefits by more than $1,000,000. The Company and its Subsidiaries shall not
withdraw, and shall cause all other ERISA Group Persons not to withdraw, in
whole or in part, from any Multiemployer Plan so as to give rise to withdrawal
liability exceeding $1,000,000 in the aggregate. At no time shall the actuarial
present value of unfunded liabilities for post-employment health care benefits
(other than COBRA continuation coverage benefits), whether or not provided under
a Plan, calculated in a manner consistent with Statement No. 106 of the
Financial Accounting Standards Board, exceed $1,000,000.

     6.17.     Transactions with Affiliates.  Neither the Company nor any of its
               ----------------------------                                     
Subsidiaries shall effect any transaction with any of their respective
Affiliates (except for the Company and its Subsidiaries) on a basis less
favorable to the Company and its Subsidiaries than would be the case if such
transaction had been effected with a non-Affiliate.

     6.18.     Interest Rate Protection.  Within 90 days after the Initial 
               ------------------------
Closing Date, each of the Borrowers shall obtain and thereafter keep in effect
one or more Interest Rate Protection Agreements conforming to International
Securities Dealers Association standards, each in form and substance reasonably
satisfactory to the Agent, covering a notional amount of at least 50% of the
Loan, in each case for an aggregate period of not less than three years.

     6.19.     Environmental Laws.
               ------------------ 

               6.19.1.   Compliance with Law and Permits.  Each of the Company 
                         -------------------------------      
     and its Subsidiaries shall use and operate all of its facilities and
     properties in material compliance with all Environmental Laws, keep in
     effect all necessary permits, approvals, certificates, licenses and other
     authorizations relating to environmental matters and remain in material
     compliance therewith, and handle all Hazardous Materials in material
     compliance with all applicable Environmental Laws.

               6.19.2.   Notice of Claims, etc.  Each of the Company and its 
                         --------------------- 
     Subsidiaries shall immediately notify the Agent, and provide copies upon
     receipt, of all written claims, complaints, notices or inquiries from
     governmental authorities relating to the condition of its facilities and
     properties or compliance with Environmental Laws, and shall promptly 

                                      -71-
<PAGE>
 
     cure and have dismissed with prejudice to the reasonable satisfaction of
     the Agent any actions and proceedings relating to compliance with
     Environmental Laws.

     6.20.     Tower Matters.
               --------------

               6.20.1.   Tower Construction Requirements.  Prior to 
                         --------------------------------  
     commencement of construction of any Tower to be owned by the Company or any
     of its Subsidiaries, the Company shall enter into a lease or license
     agreement with respect to such Tower with a licensed cellular or broadcast
     operator, PCS A-F Block Provider, ESMR Operator or other FCC or CRTC
     licensed wireless provider as the anchor tenant, which anchor tenant shall
     be reasonably acceptable to the Agent; provided, however, that the 
                                            --------  ------- 
     Company and its Subsidiaries may make Capital Expenditures and Investments
     not exceeding $1,000,000 at any one time outstanding with respect to Towers
     that are not subject to such a lease or license agreement.

               6.20.2.   No Removal of Towers.  None of the Towers located on 
                         --------------------       
     Designated Real Property shall be removed from their locations without the
     prior written consent of the Required Lenders, which consent shall not be
     unreasonably withheld or delayed, unless: (a) (i) such removal is in the
     ordinary course of business, (ii) such actions and filings of record as may
     be necessary to continue the first priority perfected Lien of the Lenders
     in the real property or leasehold upon which such Tower is finally located
     have been taken and (iii) in the case of leaseholds, the Agent has received
     Estoppel and Consent Letters relating to the new locations, or (b) such
     removal is necessary to satisfy any Legal Requirement or a properly issued
     order or mandate of any governmental authority or (c) any Tower so removed
     has been damaged and the Lenders have required the insurance proceeds
     relating thereto be applied to repayment of the Loan in accordance with
     Section 4.3.3.

               6.20.3.   Pledged Towers.  For each period of four consecutive 
                         --------------  
     fiscal quarters of the Company, commencing with the fiscal quarter ending
     August 31, 1998, Pledged Towers as of the end of such period shall have
     contributed at least 85% of Consolidated Tower Revenues.

               The Company and its Subsidiaries shall have the right to obtain
     releases and discharges of any Mortgages and Estoppel and Consent Letters
     with respect to Pledged Towers upon 10 Banking Days prior notice to the
     Agent so long as after giving effect to any such releases and discharges
     Pledged Towers shall have contributed at least 85% of Consolidated Tower
     Revenues for the period of four consecutive fiscal quarters of the Company
     then most recently ended.

               With respect to each Pledged Tower, the Obligors shall have duly
     authorized, executed, acknowledged and delivered to the Agent a mortgage
     (or deed of trust or Canadian debenture or mortgage) on each real property
     on which such Pledged Tower is

                                      -72-
<PAGE>
 
     located in substantially the form of Exhibit 6.20.3A and a leasehold
     mortgage (or leasehold deed of trust or Canadian debenture or mortgage) on
     each real property leased by the Company and its Subsidiaries on which such
     Pledged Tower is located in substantially the form of Exhibit 6.20.3B, with
     Estoppel and Consent Letters from the lessors in substantially the form of
     Exhibit 6.20.3C (each, an "Estoppel and Consent Letter"), lessor waivers
                                ----------------------------     
     and any other documents required to allow for the recording or filing of a
     leasehold mortgage, in each case in form and substance reasonably
     satisfactory to the Agent, together with, for each such real property: (a)
     copies of title insurance policies to the extent obtained by the Company or
     any of its Subsidiaries, (b) to the extent obtained by the Company or any
     of its Subsidiaries, an environmental site assessment report in such form,
     with such conclusions and from such environmental engineering firm as are
     reasonably satisfactory to the Agent, (c) to the extent obtained by the
     Company or any of its Subsidiaries, a survey on such real property that is
     reasonably satisfactory to the Agent and (d) a legal opinion of local
     counsel with respect to the recording and enforceability of such mortgages
     and leasehold mortgages in substantially the form of Exhibit 6.20.3D.

7.   Representations and Warranties.  In order to induce the Lenders to extend
     ------------------------------                                           
credit to the Borrowers hereunder, each of the Company, the Borrowers and the
other Guarantors jointly and severally represents and warrants as follows:

     7.1.      Organization and Business.
               ------------------------- 

               7.1.1.    The Company.  The Company is a duly organized and 
                         -----------      
     validly existing corporation, in good standing under the laws of
     Washington, with all power and authority, corporate or otherwise, necessary
     to (a) enter into and perform this Agreement and each other Credit Document
     to which it is party, (b) guarantee the Credit Obligations, (c) grant the
     Agent for the benefit of the Lenders the security interests in the Credit
     Security owned by it to secure the Credit Obligations and (d) own its
     properties and carry on the business now conducted or proposed to be
     conducted by it. Certified copies of the Charter and By-laws of the Company
     have been previously delivered to the Agent and are correct and complete.
     Exhibit 7.1, as from time to time hereafter supplemented in accordance with
     Sections 6.4.1 and 6.4.2, sets forth, as of the later of the date hereof or
     the end of the most recent fiscal quarter for which financial statements
     are required to be furnished in accordance with such Sections, (i) the
     jurisdiction of incorporation of the Company, (ii) the address of the
     Company's principal executive office and chief place of business, (iii)
     each name, including any trade name, under which the Company conducts its
     business and (iv) the jurisdictions in which the Company keeps tangible
     personal property.

               7.1.2.    Subsidiaries.  Each Subsidiary of the Company is duly 
                         ------------  
     validly existing and in good standing under the laws of the jurisdiction in
     which it is organized, with all power and authority, corporate or
     otherwise, necessary to (a) enter

                                      -73-
<PAGE>
 
     into and perform this Agreement and each other Credit Document to which it
     is party, (b) guarantee (in the case of the Borrowers, incur) the Credit
     Obligations, (c) grant the Agent for the benefit of the Lenders the
     security interest in the Credit Security owned by such Subsidiary to secure
     the Credit Obligations and (d) own its properties and carry on the business
     now conducted or proposed to be conducted by it. Certified copies of the
     Charter and By-laws of each Subsidiary of the Company have been previously
     delivered to the Agent and are correct and complete. Exhibit 7.1, as from
     time to time hereafter supplemented in accordance with Sections 6.4.1 and
     6.4.2, sets forth, as of the later of the date hereof or the end of the
     most recent fiscal quarter for which financial statements are required to
     be furnished in accordance with such Sections, (i) the name and
     jurisdiction of organization of each Subsidiary of the Company, (ii) the
     address of the chief executive office and principal place of business of
     each such Subsidiary, (iii) each name under which each such Subsidiary
     conducts its business, (iv) each jurisdiction in which each such Subsidiary
     keeps tangible personal property, and (v) the number of authorized and
     issued shares and ownership of each such Subsidiary.

               7.1.3.    Qualification.  Each of the Company and its 
                         -------------     
     Subsidiaries is duly and legally qualified to do business as a foreign
     corporation or other entity and is in good standing in each state or
     jurisdiction in which such qualification is required and is duly
     authorized, qualified and licensed under all laws, regulations, ordinances
     or orders of public authorities, or otherwise, to carry on its business in
     the places and in the manner in which it is conducted, except for failures
     to be so qualified, authorized or licensed which would not in the aggregate
     result, or create a material risk of resulting, in any Material Adverse
     Change.

               7.1.4.    Capitalization.  No options, warrants, conversion 
                         --------------   
     rights, preemptive rights or other statutory or contractual rights to
     purchase shares of capital stock or other securities of any Subsidiary now
     exist, nor has any Subsidiary authorized any such right, nor is any
     Subsidiary obligated in any other manner to issue shares of its capital
     stock or other securities.

     7.2       Financial Statements and Other Information; Material Agreements.
               --------------------------------------------------------------- 

               7.2.1.    Financial Statements and Other Information.  The 
                         ------------------------------------------    
     Company has previously furnished to the Lenders copies of the following:

               (a)  The audited Consolidated and unaudited Consolidating balance
     sheets of the Company and its Subsidiaries as at February 29, 1996,
     February 28, 1997 and February 28, 1998 and the audited Consolidated and
     unaudited Consolidating statements of income and the audited Consolidated
     statements of changes in shareholders' equity and of cash flows of the
     Company and its Subsidiaries for the fiscal years of the Company then
     ended.

                                      -74-
<PAGE>
 
               (b)  The Company's report on 10-K for its fiscal year ended
     February 28, 1998, as filed with the Securities and Exchange Commission.

               (c)  The seven-year financial and operational projections for the
     Company and its Subsidiaries dated April 20, 1998.

               (d)  Calculations with respect to the Computation Covenants as of
     the end of the most recent month preceding the date hereof on a pro forma
     basis giving effect to the incurrence of the Credit Obligations.

               (e)  Information Memorandum, presented by U.S. Bank, dated March
     1998, with respect to a $75,000,000 Senior Secured Credit Facility (the
     "Information Memorandum").
      ----------------------   

               The audited Consolidated financial statements (including the
     notes thereto) referred to in clause (a) above were prepared in accordance
     with GAAP and fairly present in all material respects the financial
     position of the Company and its Subsidiaries on a Consolidated basis at the
     respective dates thereof and the results of their operations for the
     periods covered thereby. The unaudited Consolidating financial statements
     referred to in clause (a) above were prepared in accordance with GAAP and
     fairly present in all material respects the financial position of the
     Company and its Subsidiaries at the respective dates thereof and the
     results of their operations for the periods covered thereby, subject to
     normal year-end audit adjustments and the addition of footnotes in the case
     of interim financial statements. Neither the Company nor any of its
     Subsidiaries has any known contingent liability material to the Company and
     its Subsidiaries on a Consolidated basis which is not reflected in the
     balance sheets referred to in clause (a) above (or delivered pursuant to
     Sections 6.4.1 or 6.4.2) or in the notes thereto.

               As to the Company and its Subsidiaries taken as a whole, to the
     knowledge of the Company, the Form 10-K referred to in clause (b) above did
     not contain any untrue statement of material fact or omit to state a
     material fact necessary in order to make the statements contained therein
     not misleading in the light of the circumstances under which they were
     made.

               The financial and operational projections referred to in clause
     (c) above conform with the internal operating forecasts of the Company and
     constitute a reasonable estimate by the Company as of the date hereof of
     its future performance, it being understood that any projected financial
     information represents an estimate, based on various assumptions, of future
     results of operations which may or may not in fact occur.

               As of the date thereof, the Information Memorandum did not
     contain any untrue statement of a material fact or omit to state a material
     fact necessary in order to make the statements contained therein not
     misleading in light of the circumstances under which

                                      -75-
<PAGE>
 
     they were made; provided, however, that the descriptions in the 
                     --------  ------- 
     Information Memorandum of other documents and agreements are intended to be
     summaries only and do not provide comprehensive descriptions of the terms
     and conditions contained in such documents and agreements.

               7.2.2.  Material Agreements.  The Company has previously 
                       -------------------   
     furnished to the Lenders correct and complete copies, including all
     exhibits, schedules and amendments thereto, of the agreements and
     instruments, each as in effect on the date hereof, listed in Exhibit 7.2.2,
     which constitute all agreements and instruments material to the Company and
     its Subsidiaries on a Consolidated basis (the "Material Agreements").
                                                    -------------------      

     7.3.      Agreements Relating to Financing Debt, Investments, etc.  Exhibit
               -------------------------------------------------------          
7.3, as from time to time hereafter supplemented in accordance with Sections
6.4.1 and 6.4.2, sets forth:

               7.3.1.  The amounts (as of the dates indicated in Exhibit 7.3, as
     so supplemented) of all Financing Debt of the Company and its Subsidiaries
     and all agreements which relate to such Financing Debt.

               7.3.2.  All Liens and Guarantees with respect to such Financing
     Debt.

               7.3.3.  All agreements which directly or indirectly require the
     Company or any Subsidiary to make any Investment.

               7.3.4.  Material license agreements with respect to the products
     of the Company and its Subsidiaries, including the parties thereto and the
     expiration dates thereof.

               7.3.5.  All trademarks, tradenames, service marks, service names
     and patents owned by the Company and its Subsidiaries that are registered
     with the federal Patent and Trademark Office (or the equivalent Canadian
     governmental office) (or with respect to which applications for such
     registration have been filed).

               7.3.6.  All copyrights owned by the Company and its Subsidiaries
     that are registered with the federal Copyright Office (or the equivalent
     Canadian governmental office).

               7.3.7.  The approximate amount and scope of accounts receivable
     owing from federal, state, provincial and local governmental authorities.

               7.3.8.  All bank and deposit accounts owned by the Company and
     its Subsidiaries.

The Company has furnished the Lenders correct and complete copies of any
agreements described in clauses (a) through (e) above requested by the Required
Lenders.

                                      -76-
<PAGE>
 
     7.4       Changes in Condition.  Since February 28, 1998, no Material 
               --------------------
Adverse Change has occurred and between February 28, 1998, and the date hereof,
neither the Company nor any Subsidiary of the Company has entered into any
material transaction outside the ordinary course of business except for the
transactions contemplated by this Agreement and the Material Agreements.
 
     7.5       Title to Assets.  The Company and its Subsidiaries have good and
               ---------------                                                 
marketable title to all assets necessary for or used in the operations of their
business as now conducted by them and reflected in the most recent balance sheet
referred to in Section 7.2.1 (or the balance sheet most recently furnished to
the Lenders pursuant to Sections 6.4.1 or 6.4.2), and to all assets acquired
subsequent to the date of such balance sheet, subject to no Liens except for
Liens permitted by Section 6.8 and except for assets disposed of as permitted by
Section 6.11.

     7.6       Operations in Conformity With Law, etc.  The operations of the
               --------------------------------------                        
Company and its Subsidiaries as now conducted or proposed to be conducted are
not in violation of, nor is the Company or its Subsidiaries in default under,
any Legal Requirement presently in effect, except for such violations and
defaults as do not and will not, in the aggregate, result, or create a material
risk of resulting, in any Material Adverse Change.  The Company has received no
notice of any such violation or default and has no knowledge of any basis on
which the operations of the Company or its Subsidiaries, as now conducted and as
currently proposed to be conducted after the date hereof, would be held so as to
violate or to give rise to any such violation or default.

     7.7       Litigation.  No litigation, at law or in equity, or any 
               ----------  
proceeding before any court, board or other governmental or administrative
agency or any arbitrator is pending or, to the knowledge of the Company, the
Borrowers or any Guarantor, threatened which involves any material risk of any
final judgment, order or liability which, after giving effect to any applicable
insurance, has resulted, or creates a material risk of resulting, in any
Material Adverse Change or which seeks to enjoin the consummation, or which
questions the validity, of any of the transactions contemplated by this
Agreement or any other Credit Document. No judgment, decree or order of any
court, board or other governmental or administrative agency or any arbitrator
has been issued against or binds the Company or any of its Subsidiaries which
has resulted, or creates a material risk of resulting, in any Material Adverse
Change.

     7.8       Authorization and Enforceability.  Each of the Company and each 
               --------------------------------   
other Obligor has taken all corporate action required to execute, deliver and
perform this Agreement and each other Credit Document to which it is party. No
consent of stockholders of the Company is necessary in order to authorize the
execution, delivery or performance of this Agreement or any other Credit
Document to which the Company is party. Each of this Agreement and each other
Credit Document constitutes the legal, valid and binding obligation of each
Obligor party thereto and is enforceable against such Obligor in accordance with
its terms.

                                      -77-
<PAGE>
 
     7.9.      No Legal Obstacle to Agreements.  Neither the execution and 
               -------------------------------    
delivery of this Agreement or any other Credit Document, nor the making of any
borrowings hereunder, nor the guaranteeing of the Credit Obligations, nor the
securing of the Credit Obligations with the Credit Security, nor the
consummation of any transaction referred to in or contemplated by this Agreement
or any other Credit Document, nor the fulfillment of the terms hereof or thereof
or of any other agreement, instrument, deed or lease contemplated by this
Agreement or any other Credit Document, has constituted or resulted in or will
constitute or result in:

               (a)  any breach or termination of the provisions of any
     agreement, instrument, deed or lease to which the Company, any of its
     Subsidiaries or any other Obligor is a party or by which it is bound, or of
     the Charter or By-laws of the Company, any of its Subsidiaries or any other
     Obligor;

               (b)  the violation of any law, statute, judgment, decree or
     governmental order, rule or regulation applicable to the Company, any of
     its Subsidiaries or any other Obligor;

               (c)  the creation under any agreement, instrument, deed or lease
     of any Lien (other than Liens on the Credit Security which secure the
     Credit Obligations) upon any of the assets of the Company, any of its
     Subsidiaries or any other Obligor; or

               (d)  any redemption, retirement or other repurchase obligation of
     the Company, any of its Subsidiaries or any other Obligor under any
     Charter, By-law, agreement, instrument, deed or lease.

No approval, authorization or other action by, or declaration to or filing with,
any governmental or administrative authority or any other Person is required to
be obtained or made by the Company, any of its Subsidiaries or any other Obligor
in connection with the execution, delivery and performance of this Agreement or
any other Credit Document, the transactions contemplated hereby or thereby, the
making of any borrowing hereunder, the guaranteeing of the Credit Obligations or
the securing of the Credit Obligations with the Credit Security (other than
filings necessary to perfect the Agent's security interest in the Credit
Security).

     7.10.     Defaults.  Neither the Company nor any of its Subsidiaries is in
               --------                                                        
default under any provision of its Charter or By-laws or of this Agreement or
any other Credit Document. Neither the Company nor any of its Subsidiaries is in
default under any provision of any agreement, instrument, deed or lease to which
it is party or by which it or its property is bound so as to result, or create a
material risk of resulting, in any Material Adverse Change.
 
     7.11.     Licenses, etc.  The Company and its Subsidiaries have all 
               -------------       
patents, patent applications, patent licenses, patent rights, trademarks,
trademark rights, trade names, trade name rights, copyrights, licenses,
franchises, permits, authorizations and other rights as are reasonably necessary
for the conduct of the business of the Company and its Subsidiaries as now
conducted by them. All of the foregoing are in full force and effect in all
material respects, and each of the

                                      -78-
<PAGE>
 
Company and its Subsidiaries is in substantial compliance with the foregoing
without any known conflict with the valid rights of others which has resulted,
or creates a material risk of resulting, in any Material Adverse Change. No
event has occurred which permits, or after notice or lapse of time or both would
permit, the revocation or termination of any such license, franchise or other
right or which affects the rights of any of the Company and its Subsidiaries
thereunder so as to result, or to create a material risk of resulting, in any
Material Adverse Change.
 
     7.12.     Tax Returns.  Each of the Company and its Subsidiaries has 
               -----------         
filed all material tax and information returns which are required to be filed by
it and has paid, or made adequate provision for the payment of, all taxes which
have or may become due pursuant to such returns or to any assessment received by
it, other than taxes and assessments being contested by the Company and its
Subsidiaries in good faith by appropriate proceedings and for which adequate
reserves have been taken in accordance with GAAP. Neither the Company nor any of
its Subsidiaries knows of any material additional assessments or any basis
therefor. The Company reasonably believes that the charges, accruals and
reserves on the books of the Company and its Subsidiaries in respect of taxes or
other governmental charges are adequate.

     7.13.     Certain Business Representations.
               -------------------------------- 

               7.13.1   Labor Relations.  No dispute or controversy between the 
                        ---------------  
     Company or any of its Subsidiaries and any of their respective employees
     has resulted, or is reasonably likely to result, in any Material Adverse
     Change, and neither the Company nor any of its Subsidiaries anticipates
     that its relationships with its unions or employees will result, or are
     reasonably likely to result, in any Material Adverse Change. The Company
     and each of its Subsidiaries is in compliance in all material respects with
     all federal, provincial and state laws with respect to (a) non-
     discrimination in employment with which the failure to comply, in the
     aggregate, has resulted, or creates a material risk of resulting, in a
     Material Adverse Change and (b) the payment of wages.

               7.13.2.  Antitrust.  Each of the Company and its Subsidiaries is 
                        ---------       
     in compliance in all material respects with all federal, provincial and
     state antitrust laws relating to its business and the geographic
     concentration of its business.

               7.13.3.  Real Property Leases.  The present and contemplated 
                        --------------------        
     use of the real property owned or leased by the Company for the operation
     of Towers is in compliance in all material respects with all applicable
     zoning ordinances and regulations and other laws and regulations where
     failure so to comply would result, or create reasonable risk of resulting,
     in a Material Adverse Change. Each Lease is in full force and effect, the
     Company or one of its Subsidiaries has all rights of the lessee thereunder,
     there has been no default in the performance of any of its terms or
     conditions by any party thereto, and no claims of default have been
     asserted with respect thereto where such default would result, or create a
     reasonable risk of resulting, in a Material Adverse Change.

                                      -79-
<PAGE>
 
               7.13.4.   FCC, CRTC and FAA Matters.  The Company (a) has duly 
                         -------------------------       
     and timely filed all material reports, registrations and other material
     filings, if any, which are required to be filed by it or any of its
     Subsidiaries under the Communications Act or any other applicable law, rule
     or regulation of any governmental authority, including the FCC, CRTC and
     the FAA, the non-filing of which would not result, or be reasonably likely
     to result, in a Material Adverse Change, and (b) is in compliance with all
     such laws, rules, regulations and ordinances, including those promulgated
     by the FCC, CRTC and the FAA, to the extent the noncompliance with which
     would result, or be reasonably likely to result, in a Material Adverse
     Change. All information provided by or on behalf of the Company or any
     Affiliate in any material filing, if any, with the FCC, CRTC and the FAA
     relating to the business of the Company and its Subsidiaries was, to the
     knowledge of such Person at the time of filing, complete and correct in all
     material respects when made, and the FCC, CRTC and the FAA have been
     notified of any substantial or significant changes in such information as
     may be required in accordance with applicable Legal Requirements.

               7.13.5.   Year 2000 Issues.  Based on a review of the 
                         ----------------      
     operations of the Company and its Subsidiaries as they relate to the
     processing, storage and retrieval of data, the Company does not believe
     that a Material Adverse Change is reasonably likely to occur as a result of
     computer software and hardware that will not function with respect to
     periods commencing or including January 1, 2000 at least as effectively as
     with respect to periods ending prior to December 31, 1999.

               7.13.6.   Future Expenditures.  Neither the Company nor any of 
                         -------------------    
     its Subsidiaries are aware of any future expenditures that will be required
     by the Company and its Subsidiaries to meet the provisions of any federal,
     state or foreign governmental statutes, orders, rules or regulations and
     that will be so burdensome as to result, or create a material risk of
     resulting, in any Material Adverse Change.

               7.13.7.   Senior Subordinated Notes.  The Company has issued 
                         -------------------------     
     the Senior Subordinated Notes for cash proceeds in a cash amount of not
     less than $14,750,000 on terms and conditions reasonably satisfactory to
     the Required Lenders, the net proceeds of which have been invested as
     equity in the U.S. Borrower.

               7.13.8.   Payment of Fees.  As of the date hereof the Company 
                         ---------------       
     has paid the fees contemplated by Section 5.1.2.

     7.14.     Environmental Regulations.
               ------------------------- 

               7.14.1    Environmental Compliance.  Each of the Company and its
                         ------------------------                              
     Subsidiaries is in compliance in all material respects with the Clean Air
     Act, the Federal Water Pollution Control Act, the Marine Protection
     Research and Sanctuaries Act, RCRA, CERCLA and any other Environmental Law
     in effect in any jurisdiction in which any

                                      -80-
<PAGE>
 
properties of the Company or any of its Subsidiaries are located or where any of
them conducts its business, and with all applicable published rules and
regulations (and applicable standards and requirements) of the federal
Environmental Protection Agency and of any similar agencies in states or foreign
countries in which the Company or its Subsidiaries conducts its business other
than those which in the aggregate have not resulted, and do not create a
material risk of resulting, in a Material Adverse Change.

       7.14.2.  Environmental Litigation.  No suit, claim, action or proceeding
                ------------------------                                       
of which the Company or any of its Subsidiaries has been given notice or
otherwise has knowledge is now pending before any court, governmental agency or
board or other forum, or to the Company's or any of its Subsidiaries knowledge,
threatened by any Person (nor to the Company's or any of its Subsidiaries'
knowledge, does any factual basis exist therefor) for, and neither the Company
nor any of its Subsidiaries have received written correspondence from any
federal, state or local governmental authority with respect to:

       (a)   noncompliance by the Company or any of its Subsidiaries with
any Environmental Law;

       (b)   personal injury, wrongful death or other tortious conduct
relating to materials, commodities or products used, generated, sold,
transferred or manufactured by the Company or any of its Subsidiaries (including
products made of, containing or incorporating asbestos, lead or other Hazardous
Material; or

       (c)   the release into the environment by the Company or any of its
Subsidiaries of any Hazardous Material generated by the Company or any of its
Subsidiaries whether or not occurring at or on a site owned, leased or operated
by the Company or any of its Subsidiaries.

       7.14.3.  Hazardous Material.  Exhibit 7.14 (as from time to time
                ------------------                                     
hereafter supplemented in accordance with Sections 6.4.1 and 6.4.2) contains a
list as of the date hereof of all waste disposal or dump sites at which
Hazardous Material generated by either the Company or any of its Subsidiaries
has been disposed of directly by the Company or any of its Subsidiaries and all
independent contractors to whom the Company and its Subsidiaries have delivered
Hazardous Material, or to the Company's or any of its Subsidiaries' knowledge,
where Hazardous Material finally came to be located, and indicates all such
sites which are or have been included (including as a potential or suspect site)
in any published federal, state or local "superfund" or other list of hazardous
or toxic waste sites.  Any waste disposal or dump sites at which Hazardous
Material generated by either the Company or any of its Subsidiaries has been
disposed of directly by the Company or any of its Subsidiaries and all
independent contractors to whom the Company or any of its Subsidiaries have
delivered Hazardous Material, or to the Company's or any of its Subsidiaries'
knowledge, where Hazardous Material finally came 

                                      -81-
<PAGE>
 
     to be located, has not resulted, and does not create a material risk of
     resulting, in a Material Adverse Change.

            7.14.4. Environmental Condition of Properties. None of the
                    -------------------------------------
     properties owned or leased by the Company or any of its Subsidiaries has
     been used as a treatment, storage or disposal site for Hazardous Material,
     other than as disclosed in Exhibit 7.14 (as from time to time hereafter
     supplemented in accordance with Sections 6.4.1 and 6.4.2). No Hazardous
     Material is present in any real property currently or formerly owned or
     operated by the Company or any of its Subsidiaries except that which has
     not resulted, and does not create a material risk of resulting, in a
     Material Adverse Change.

     7.15.  Pension Plans.  Each Plan (other than a Multiemployer Plan) and, to
            -------------                                                      
the knowledge of the Company and its Subsidiaries, each Multiemployer Plan is in
material compliance with the applicable provisions of ERISA and the Code.  Each
Multiemployer Plan and each Plan that constitutes a "defined benefit plan" (as
defined in ERISA) are set forth in Exhibit 7.15 (as from time to time hereafter
supplemented in accordance with Sections 6.4.1 and 6.4.2).  Each ERISA Group
Person has met all of the funding standards applicable to all Plans that are not
Multiemployer Plans, and no condition exists which would permit the institution
of proceedings to terminate any Plan that is not a Multiemployer Plan under
section 4042 of ERISA.  To the knowledge of the Company and each Subsidiary, no
Plan that is a Multiemployer Plan is currently insolvent or in reorganization or
has been terminated within the meaning of ERISA.

     7.16.  Government Regulation; Margin Stock.
            ----------------------------------- 

            7.16.1.  Government Regulation.  Neither the Company nor any of its
                     ---------------------                                     
     Subsidiaries, nor any Person controlling the Company or any of its
     Subsidiaries or under common control with the Company or any of its
     Subsidiaries, is subject to regulation under the Public Utility Holding
     Company Act of 1935, the Federal Power Act, the Investment Company Act, the
     Interstate Commerce Act or any statute or regulation which regulates the
     incurring by the Company or any of its Subsidiaries of Financing Debt as
     contemplated by this Agreement and the other Credit Documents.

            7.16.2. Margin Stock. Neither the Company nor any of its
                    ------------
     Subsidiaries owns any Margin Stock.

     7.17.  Disclosure. Neither this Agreement nor any other Credit Document nor
            ----------
any financial statement, report, notice, mortgage, assignment or certificate
furnished or to be furnished to the Lenders or the Agent by or on behalf of the
Company or any of its Subsidiaries in connection with the transactions
contemplated hereby or by such Credit Document, taken as a whole, contains any
untrue statement of material fact or omits to state a material fact necessary in
order to make the statements contained herein or therein not misleading in light
of the circumstances under which they were made.

                                      -82-
<PAGE>
 
8.   Defaults.
     -------- 

     8.1.  Events of Default.  The following events are referred to as "Events
           -----------------                                            ------
of Default":
----------  

           8.1.1. Payment.  The U.S. Borrower or the Canadian Borrower, as the
                  -------                                                     
case may be, shall fail to make any payment in respect of:  (a) interest or any
fee on or in respect of any of the Credit Obligations owed by it as the same
shall become due and payable, and such failure shall continue for a period of
three Banking Days, or (b) any Credit Obligation with respect to payments made
by any Letter of Credit Issuer under any Letter of Credit or any draft drawn
thereunder within three Banking Days after demand therefor by such Letter of
Credit Issuer or (c) principal of any of the Credit Obligations owed by it
(including any amount with respect to a Bankers' Acceptance) as the same shall
become due, whether at maturity or by acceleration or otherwise.

           8.1.2. Specified Covenants.  The Company or any of its Subsidiaries
                  -------------------                                         
shall fail to perform or observe any of the provisions of Section 6.4.5 or
Sections 6.5 through 6.17 or Section 6.20.

           8.1.3.  Other Covenants.  The Company, any of its Subsidiaries or any
                   ---------------                                              
other Obligor shall fail to perform or observe any other covenant, agreement or
provision to be performed or observed by it under this Agreement or any other
Credit Document, and such failure shall not be rectified or cured to the written
satisfaction of the Required Lenders within 30 days after the earlier of (a)
notice thereof by the Agent to the Company or (b) a Financial Officer shall have
actual knowledge thereof.

           8.1.4.  Representations and Warranties. Any material representation
                   ------------------------------
or warranty of or with respect to the Company, any of its Subsidiaries or any
other Obligor made to the Lenders or the Agent in, pursuant to or in connection
with this Agreement or any other Credit Document, or in any financial statement,
report, notice, mortgage, assignment or certificate delivered to the Agent or
any of the Lenders by the Company, any of its Subsidiaries or any other Obligor
in connection herewith or therewith, shall be false in any material respect on
the date as of which it was made.

           8.1.5. Material Financing Debt Cross Default, etc.
                  ------------------------------------------ 

           (a)   The Company or any of its Subsidiaries shall fail to make any
     payment when due (after giving effect to any applicable grace periods) in
     respect of any Material Financing Debt;

           (b)   the Company or any of its Subsidiaries shall fail to perform or
     observe the terms of any agreement or instrument relating to any Material
     Financing Debt, and such failure shall continue, without having been duly
     cured, waived or consented to, beyond 

                                      -83-
<PAGE>
 
     the period of grace, if any, specified in such agreement or instrument, and
     such failure shall permit the acceleration of such Material Financing Debt;

           (c)   all or any part of any Material Financing Debt of the Company
     or any of its Subsidiaries shall be accelerated or shall become due or
     payable prior to its stated maturity (except with respect to voluntary
     prepayments thereof) for any reason whatsoever;

           (d)   any Lien on any property of the Company or any of its
     Subsidiaries securing any Material Financing Debt shall be enforced by
     foreclosure or similar action; or

           (e)   any holder of any Material Financing Debt shall exercise any
     right of rescission with respect  to the issuance thereof or put, mandatory
     prepayment or repurchase rights against any Obligor with respect to such
     Material Financing Debt (other than any such rights that may be satisfied
     with "payment in kind" notes or other similar securities).

           8.1.6. Ownership; Liquidation; etc.  Except as permitted by Section
                  ---------------------------                                 
     6.11:

           (a)   the Company shall cease to own, directly or indirectly, all the
     capital stock of its Subsidiaries, except to the extent permitted by
     Section 6.12.1; or

           (b)   Either Calvin J. Payne or S. Roy Jeffrey shall cease to be
     actively involved in the executive management of the Company and a
     replacement reasonably satisfactory to the Required Lenders shall not have
     been selected within 180 days; or

           (c)   any Person, together with "affiliates" and "associates" of such
     Person within the meaning of Rule 12b-2 of the Exchange Act, or any "group"
     including such Person under sections 13(d) and 14(d) of the Exchange Act,
     other than the Persons described in paragraph (b) above, shall acquire
     after the date hereof beneficial ownership within the meaning of Rule 13d-3
     of the Exchange Act of 33% or more of either the voting stock or total
     equity capital of the Company; or

           (d)   a "Change of Control Event" as defined in the Senior
     Subordinated Notes Purchase Agreement shall occur; or

           (e)   the Company or any of its Subsidiaries or any other Obligor
     shall initiate any action to dissolve, liquidate or otherwise terminate its
     existence.

          8.1.7. Enforceability, etc.  Any Credit Document shall cease for any
                 -------------------                                          
reason (other than the scheduled termination thereof in accordance with its
terms) to be enforceable in accordance with its terms or in full force and
effect, except to the extent 

                                      -84-
<PAGE>
 
caused by any action or inaction of the Agent or any Lender; or any party (other
than the Agent or any Lender) to any Credit Document shall so assert in a
judicial or similar proceeding; or the security interests created by this
Agreement or any other Credit Documents shall cease to be enforceable and of the
same effect and priority purported to be created hereby except to the extent
caused by any action or inaction of the Agent or any Lender.

           8.1.8.  Judgments. A final judgment (a) which, with other outstanding
                   ---------
final judgments against the Company and its Subsidiaries, exceeds an aggregate
of $500,000 in excess of applicable insurance coverage shall be rendered against
the Company or any of its Subsidiaries, or (b) which grants injunctive relief
that results, or creates a material risk of resulting, in a Material Adverse
Change and in either case if (i) within 30 days after entry thereof, such
judgment shall not have been discharged or execution thereof stayed pending
appeal or (ii) within 30 days after the expiration of any such stay, such
judgment shall not have been discharged.

           8.1.9.  ERISA.  Any "reportable event" (as defined in section 4043 of
                   -----                                                        
ERISA) shall have occurred that reasonably could be expected to result in
termination of a Plan or the appointment by the appropriate United States
District Court of a trustee to administer any Plan or the imposition of a Lien
in favor of a Plan; or any ERISA Group Person shall fail to pay when due amounts
aggregating in excess of $1,000,000 which it shall have become liable to pay to
the PBGC or to a Plan under Title IV of ERISA; or notice of intent to terminate
a Plan shall be filed under Title IV of ERISA by any ERISA Group Person or
administrator; or the PBGC shall institute proceedings under Title IV of ERISA
to terminate or to cause a trustee to be appointed to administer any Plan or a
proceeding shall be instituted by a fiduciary of any Plan against any ERISA
Group Person to enforce section 515 or 4219(c)(5) of ERISA and such proceeding
shall not have been dismissed within 30 days thereafter; or a condition shall
exist by reason of which the PBGC would be entitled to obtain a decree
adjudicating that any Plan must be terminated.

           8.1.10. Bankruptcy, etc.  The Company, any of its Subsidiaries or any
                   ---------------                  
other Obligor shall:

           (a)   commence a voluntary case under the Bankruptcy Code or
     authorize, by appropriate proceedings of its board of directors or other
     governing body, the commencement of such a voluntary case;

           (b)   (i) have filed against it a petition commencing an involuntary
     case under the Bankruptcy Code that shall not have been dismissed within 60
     days after the date on which such petition is filed, or (ii) file an answer
     or other pleading within such 60-day period admitting or failing to deny
     the material allegations of such a petition or seeking, consenting to or
     acquiescing in the relief therein provided, or (iii) have entered against
     it an order for relief in any involuntary case commenced under the
     Bankruptcy Code;

                                      -85-
<PAGE>
 
           (c)   seek relief as a debtor under any applicable law, other than
     the Bankruptcy Code, of any jurisdiction relating to the liquidation or
     reorganization of debtors or to the modification or alteration of the
     rights of creditors, or consent to or acquiesce in such relief;

           (d)   have entered against it an order by a court of competent
     jurisdiction (i) finding it to be bankrupt or insolvent, (ii) ordering or
     approving its liquidation or reorganization as a debtor or any modification
     or alteration of the rights of its creditors or (iii) assuming custody of,
     or appointing a receiver or other custodian for, all or a substantial
     portion of its property; or

           (e)   make an assignment for the benefit of, or enter into a
     composition with, its creditors, or appoint, or consent to the appointment
     of, or suffer to exist a receiver or other custodian for, all or a
     substantial portion of its property.

     8.2.  Certain Actions Following an Event of Default.  If any one or more
           ---------------------------------------------                     
Events of Default shall occur, then in each and every such case:

           8.2.1. Terminate Obligation to Extend Credit. Upon written request of
                  -------------------------------------
the Required Lenders, the Agent shall terminate the obligations of the Lenders
to make any further extensions of credit under the Credit Documents by
furnishing notice of such termination to the Borrowers; provided, however, that
if a Bankruptcy Default shall have occurred, the obligations of the Lenders to
make any further extensions of credit under the Credit Documents shall
automatically terminate.

           8.2.2. Specific Performance; Exercise of Rights. Upon written request
                  ---------------------------------------- 
of the Required Lenders, the Agent shall proceed to protect and enforce the
Lenders' rights by suit in equity, action at law and/or other appropriate
proceeding, either for specific performance of any covenant or condition
contained in this Agreement or any other Credit Document (other than Interest
Rate Protection Agreements) or in any instrument or assignment delivered to the
Lenders pursuant to this Agreement or any other Credit Document (other than
Interest Rate Protection Agreements), or in aid of the exercise of any power
granted in this Agreement or any other Credit Document (other than Interest Rate
Protection Agreements) or any such instrument or assignment.

           8.2.3. Acceleration. Upon written request of the Required Lenders,
                  ------------
the Agent shall by notice in writing to the Borrowers (a) declare all or any
part of the unpaid balance of the Credit Obligations (other than amounts under
Interest Rate Protection Agreements) then outstanding to be immediately due and
payable, (b) require the U.S. Borrower immediately to deposit with the Agent in
cash an amount equal to the then Letter of Credit Exposure (which cash shall be
held and applied as provided in Section 4.4), and (c) require the Canadian
Borrower immediately to deposit with the Canadian

                                      -86-
<PAGE>
 
     Lender in cash in Canadian Funds an amount equal to the aggregate full face
     amount of all outstanding Bankers' Acceptances (which cash shall be held
     and applied as provided in Section 4.5), and thereupon such unpaid balance
     or part thereof and such amount equal to the Letter of Credit Exposure and
     aggregate full face amount of all outstanding Bankers' Acceptances shall
     become so due and payable without presentation, protest or further demand
     or notice of any kind, all of which are hereby expressly waived; provided,
                                                                      --------
     however, that if a Bankruptcy Default shall have occurred, the unpaid
     -------
     balance of the Credit Obligations (other than amounts under Interest Rate
     Protection Agreements) shall automatically become immediately due and
     payable.

          8.2.4. Enforcement of Payment; Credit Security; Setoff.  Upon written
                 -----------------------------------------------               
     request of the Required Lenders, the Agent shall proceed to enforce payment
     of the Credit Obligations in such manner as it may elect, to cancel, or
     instruct other Letter of Credit Issuers to cancel, any outstanding Letters
     of Credit which permit the cancellation thereof and to realize upon any and
     all rights in the Credit Security. The Lenders may offset and apply toward
     the payment of the Credit Obligations (and/or toward the curing of any
     Event of Default) any Indebtedness from the Lenders to the respective
     Obligors, including any Indebtedness represented by deposits in any account
     maintained with the Lenders, regardless of the adequacy of any security for
     the Credit Obligations. The Lenders shall have no duty to determine the
     adequacy of any such security in connection with any such offset.

          8.2.5. Cumulative Remedies. To the extent not prohibited by applicable
                 -------------------                                     
     law which cannot be waived, all of the Lenders' rights hereunder and under
     each other Credit Document shall be cumulative.

     8.3.  Annulment of Defaults.  Once an Event of Default has occurred, such
           ---------------------                                              
Event of Default shall be deemed to exist and be continuing for all purposes of
the Credit Documents (other than Interest Rate Protection Agreements) until the
Required Lenders or the Agent (with the consent of the Required Lenders) shall
have waived such Event of Default in writing, stated in writing that the same
has been cured to such Lenders' reasonable satisfaction or entered into an
amendment to this Agreement which by its express terms cures such Event of
Default, at which time such Event of Default shall no longer be deemed to exist
or to have continued.  No such action by the Lenders or the Agent shall extend
to or affect any subsequent Event of Default or impair any rights of the Lenders
upon the occurrence thereof.  The making of any extension of credit during the
existence of any Default or Event of Default shall not constitute a waiver
thereof.

     8.4.  Waivers.  To the extent that such waiver is not prohibited by the
           -------                                                          
provisions of applicable law that cannot be waived, each of the Company and the
other Obligors waives:

                                      -87-
<PAGE>
 
           (a)   all presentments, demands for performance, notices of
     nonperformance (except to the extent required by this Agreement or any
     other Credit Document), protests, notices of protest and notices of
     dishonor;

           (b)   any requirement of diligence or promptness on the part of the
     Agent or any Lender in the enforcement of its rights under this Agreement
     or any other Credit Document; and

           (c)   any and all notices of every kind and description which may be
     required to be given by any statute or rule of law.

 9.  Expenses; Indemnity.
     ------------------- 

     9.1.  Expenses.  Whether or not the transactions contemplated hereby shall
           --------                                                            
be consummated, the Borrowers will pay:

           (a)   all reasonable expenses of the Agent and the Syndication Agent
     (including the out-of-pocket expenses related to forming the group of
     Lenders and reasonable fees and disbursements of the counsel to the Agent
     and the Syndication Agent) in connection with the negotiation, preparation
     and duplication of this Agreement and each other Credit Document,
     examinations by, and reports of, the Agent's commercial financial
     examiners, fixed asset appraisers and environmental consultants, the
     transactions contemplated hereby and thereby and amendments, waivers,
     consents and other operations hereunder and thereunder;

           (b)   all recording and filing fees and transfer and documentary
     stamp and similar taxes at any time payable in respect of this Agreement,
     any other Credit Document, any Credit Security or the incurrence of the
     Credit Obligations; and

           (c)   all other reasonable expenses incurred by the Agent, the
     Lenders or the holder of any Credit Obligation in connection with the
     enforcement of any rights hereunder or under any other Credit Document or
     any work-out negotiations relating to the Credit Obligations, including
     costs of collection and reasonable attorneys' fees (including a reasonable
     allowance for the hourly cost of attorneys employed by the Lenders on a
     salaried basis) and expenses.

     9.2.  General Indemnity.  Each of the Borrowers shall indemnify the Lenders
           -----------------                                                    
and the Agent and hold them harmless from any liability, loss or damage
resulting from the violation by the Borrowers of Section 2.5.  In addition, each
of the Borrowers shall indemnify each Lender, the Agent, the Syndication Agent,
each of the Lenders' or the Agent's or the Syndication Agent's directors,
officers, employees, agents, attorneys, accountants, consultants and each
Person, if any, who controls any Lender or the Agent (each Lender, the Agent and
each of such directors, officers, employees, agents, attorneys, accountants,
consultants and control Persons is referred to 

                                      -88-
<PAGE>
 
as an "Indemnified Party") and hold each of them harmless from and against any
       -----------------
and all claims, damages, liabilities and reasonable expenses (including
reasonable fees and disbursements of counsel with whom any Indemnified Party may
consult in connection therewith and all reasonable expenses of litigation or
preparation therefor) which any Indemnified Party may incur or which may be
asserted against any Indemnified Party in connection with (a) the Indemnified
Party's compliance with or contest of any subpoena or other process issued
against it in any proceeding involving the Company or any of its Subsidiaries or
their Affiliates, (b) any litigation or investigation involving the Company, any
of its Subsidiaries or their Affiliates, or any officer, director or employee
thereof, (c) the existence or exercise of any security rights with respect to
the Credit Security in accordance with the Credit Documents, or (d) this
Agreement, any other Credit Document or any transaction contemplated hereby or
thereby; provided, however, that the foregoing indemnity shall not apply (i) to
         --------  -------
litigation commenced by either of the Borrowers against the Lenders or the Agent
or the Syndication Agent which seeks enforcement of any of the rights of such
Borrower hereunder or under any other Credit Document and is determined
adversely to the Lenders or the Agent or the Syndication Agent in a final
nonappealable judgment or (ii) to the extent such claims, damages, liabilities
and expenses result from the Indemnified Party's own gross negligence or willful
misconduct.

     9.3.  Indemnity with Respect to Foreign Currency Transactions.  Each of the
           -------------------------------------------------------              
U.S. Borrower and the Canadian Borrower, as the case may be, waives, to the
extent it may lawfully do so, any right it may have in any jurisdiction to pay
any Credit Obligation in a currency other than the currency in which such Credit
Obligation is expressed to be payable under the Credit Documents.  If a judgment
or order is rendered by a court or tribunal of competent jurisdiction for the
payment of any amounts owing to the Lenders under any Credit Document, or under
a judgment or order of a court of any other jurisdiction in respect thereof, and
any such judgment or order is expressed in a currency (the "Payment Currency")
                                                            ----------------  
other than the currency agreed to be payable under the Credit Documents (the
                                                                            
"Agreed Currency"), or in the event of any payment being made in any currency
 ---------------                                                             
other than the Agreed Currency whether pursuant to the enforcement of any
security interest in the Credit Security, the liquidation of the U.S. Borrower
or the Canadian Borrower, as the case may be, or otherwise, such Borrower shall,
to the extent permitted by applicable law, indemnify and hold the Lenders
harmless against any deficiency arising or resulting from any variation in rates
of exchange between (a) the rate at which any amount expressed in any Agreed
Currency for purposes of any Credit Document is converted for the purpose of any
such judgment, order or payment into an equivalent amount in the Payment
Currency, and (b) the rate at which at the time of payment of such amount
pursuant to any Credit Document such Agreed Currency could be purchased by the
Agent with the Payment Currency in the spot market in the place at which such
payment was to have been made.

     9.4.  Indemnity With Respect to Letters of Credit.  The U.S. Borrower shall
           -------------------------------------------                          
indemnify each Letter of Credit Issuer and its correspondents and hold each of
them harmless from and against any and all claims, losses, liabilities, damages
and reasonable expenses (including reasonable attorneys' fees) arising from or
in connection with any Letter of Credit, including any such claim, loss,
liability, damage or expense arising out of any transfer, sale, 

                                      -89-
<PAGE>
 
delivery, surrender or endorsement of any invoice, bill of lading, warehouse
receipt or other document at any time held by the Agent, such Letter of Credit
Issuer or held for their respective accounts by any of their correspondents, in
connection with any Letter of Credit, except to the extent such claims, losses,
liabilities, damages and expenses result from gross negligence or willful
misconduct on the part of the Agent or any other Letter of Credit Issuer.

 10. Operations; Agent.
     ----------------- 

     10.1. Interests in Credits.  The Percentage Interest of each Lender in the
           --------------------                                                
respective portions of the Loan and Letter of Credit Exposure, and the related
Commitments, shall be computed based on the maximum principal amount for each
Lender as set forth in the Register, as from time to time in effect. The current
Percentage Interests are set forth in Exhibit 10.1, which may be updated by the
Agent from time to time to conform to the Register.

     10.2. Agent's Authority to Act, etc.  Each of the Lenders appoints and
           -----------------------------                                   
authorizes BankBoston to act for the Lenders as the Lenders' Agent in connection
with the transactions contemplated by this Agreement and the other Credit
Documents (other than Interest Rate Protection Agreements) on the terms set
forth herein.  All action in connection with the enforcement of, or the exercise
of any remedies (other than the Lenders' rights of set-off as provided in
Section 8.2.4 or in any Credit Document) in respect of the Credit Obligations
and Credit Documents shall be taken by the Agent.

     10.3. Borrowers to Pay Agent, etc.  Each Borrower and each Guarantor shall
           ---------------------------                                         
be fully protected in making all payments in respect of the Credit Obligations
(other than payments under Interest Rate Protection Agreements and payments of
the Canadian Loan, which shall be made to the Canadian Lender) to the Agent, in
relying upon consents, modifications and amendments executed by the Agent
purportedly on the Lenders' behalf, and in dealing with the Agent as herein
provided.  The Agent may charge the accounts of each Borrower, on the dates when
the amounts thereof become due and payable, with the amounts of the principal of
and interest on the Revolving Loan, any amounts paid by the Letter of Credit
Issuers to third parties under Letters of Credit or drafts presented thereunder,
commitment fees, Letter of Credit fees and all other fees and amounts owing
under any Credit Document (other than Interest Rate Protection Agreements and
the Canadian Loan).  The Canadian Lender may charge the account of the Canadian
Borrower, on the dates when the amounts thereof become due and payable, with the
amounts of the principal of and interest on the Canadian Loan.

     10.4. Lender Operations for Advances, Letters of Credit, etc.
           ------------------------------------------------------ 

           10.4.1   Advances. On each Closing Date, each Lender shall advance to
                    -------- 
the Agent in immediately available funds such Lender's Percentage Interest in
the portion of the Revolving Loan advanced on such Closing Date prior to 12:00
noon (Boston time). If such funds are not received at such time, but all
applicable conditions set forth in Section 5 have been satisfied, each Lender
authorizes and requests the Agent to advance for the

                                      -90-
<PAGE>
 
Lender's account, pursuant to the terms hereof, the Lender's respective
Percentage Interest in such portion of the Revolving Loan and agrees to
reimburse the Agent in immediately available funds for the amount thereof prior
to 2:00 p.m. (Boston time) on the day any portion of the Loan is advanced
hereunder; provided, however, that the Agent is not authorized to make any such
           --------  -------
advance for the account of any Lender who has previously notified the Agent in
writing that such Lender will not be performing its obligations to make further
advances hereunder; and provided, further, that the Agent shall be under no
                        --------  -------
obligation to make any such advance.

          10.4.2. Letters of Credit. Each of the Lenders authorizes and requests
                  -----------------
each Letter of Credit Issuer to issue the Letters of Credit provided for in
Section 2.3 and to grant each Lender a participation in each of such Letters of
Credit in an amount equal to its Percentage Interest in the amount of each such
Letter of Credit. Promptly upon the request of the Letter of Credit Issuer, each
Lender shall reimburse the Letter of Credit Issuer in immediately available
funds for such Lender's Percentage Interest in the amount of all obligations to
third parties incurred by the Letter of Credit Issuer in respect of each Letter
of Credit and each draft accepted under a Letter of Credit to the extent not
reimbursed by the U.S. Borrower by 2:00 p.m. (Boston time) on the Banking Day
when due. The Letter of Credit Issuer will notify each Lender of the issuance of
any Letter of Credit, the amount and date of payment of any draft drawn or
accepted under a Letter of Credit and whether in connection with the payment of
any such draft the amount thereof was added to the Revolving Loan or was
reimbursed by the U.S. Borrower.

          10.4.3. Agent to Allocate Payments, etc. All payments of principal and
                  -------------------------------
interest in respect of the extensions of credit for the Loan made pursuant to
this Agreement, reimbursement of amounts paid by any Letter of Credit Issuer to
third parties under Letters of Credit or drafts presented thereunder, commitment
fees, Letter of Credit fees and other fees under this Agreement shall, as a
matter of convenience, be made by the Borrowers and the Guarantors to the Agent
in immediately available funds by 1:00 p.m. (Boston time) on any Banking Day,
except for payments of the Canadian Loan, which shall be made to the Canadian
Lender in immediately available funds by 1:00 p.m. (Toronto time) on any Banking
Day. The share of each Lender in the Revolving Loan and any Letter of Credit
shall be credited to such Lender by the Agent in immediately available funds by
2:00 p.m. (Boston time) on such Banking Day in such manner that the principal
amount of the Credit Obligations to be paid shall be paid proportionately in
accordance with the Lenders' respective Percentage Interests in such Credit
Obligations, except as otherwise provided in this Agreement. Under no
circumstances shall any Lender be required to produce or present its Notes as
evidence of its interests in the Credit Obligations in any action or proceeding
relating to the Credit Obligations.

          10.4.4. Delinquent Lenders; Nonperforming Lenders.  In the event that
                  -----------------------------------------                    
any Lender fails to reimburse the Agent pursuant to Sections 10.4.1 or 10.4.2
for the Percentage Interest of such lender (a "Delinquent Lender") in any credit
                                               -----------------                
advanced by the

                                      -91-
<PAGE>
 
     Agent pursuant hereto, overdue amounts (the "Delinquent Payment") due from
                                                  ------------------
     the Delinquent Lender to the Agent shall bear interest, payable by the
     Delinquent Lender on demand, at a per annum rate equal to (a) the Federal
     Funds Rate for the first three days overdue and (b) the sum of 2% plus the
     Federal Funds Rate for any longer period. Such interest shall be payable to
     the Agent for its own account for the period commencing on the date of the
     Delinquent Payment and ending on the date the Delinquent Lender reimburses
     the Agent on account of the Delinquent Payment (to the extent not paid by
     any Obligor as provided below) and the accrued interest thereon (the
     "Delinquency Period"), whether pursuant to the assignments referred to
      ------------------
     below or otherwise. Upon notice by the Agent, the U.S. Borrower or the
     Canadian Borrower, as the case may be, will pay to the Agent the principal
     (but not the interest) portion of the Delinquent Payment. During the
     Delinquency Period, in order to make reimbursements for the Delinquent
     Payment and accrued interest thereon, the Delinquent Lender shall be deemed
     to have assigned to the Agent all interest, commitment fees and other
     payments made by the U.S. Borrower or the Canadian Borrower, as the case
     may be, under Section 3 that would have thereafter otherwise been payable
     under the Credit Documents to the Delinquent Lender. During any other
     period in which any Lender is not performing its obligations to extend
     credit under Section 2 (a "Nonperforming Lender"), the Nonperforming Lender
                                --------------------
     shall be deemed to have assigned to each Lender that is not a Nonperforming
     Lender (a "Performing Lender") all principal and other payments made by the
                ------------------
     U.S. Borrower or the Canadian Borrower, as the case may be, under Section 4
     that would have thereafter otherwise been payable under the Credit
     Documents to the Nonperforming Lender. The Agent shall credit a portion of
     such payments to each Performing Lender in an amount equal to the
     Percentage Interest of such Performing Lender in an amount equal to the
     Percentage Interest of such Performing Lender divided by one minus the
                                                                  -----
     Percentage Interest of the Nonperforming Lender until the respective
     portions of the Loan owed to all the Lenders are the same as the Percentage
     Interests of the Lenders immediately prior to the failure of the
     Nonperforming Lender to perform its obligations under Section 2. The
     foregoing provisions shall be in addition to any other remedies the Agent,
     the Performing Lenders or the Borrowers may have under law or equity
     against the Delinquent Lender as a result of the Delinquent Payment or
     against the Nonperforming Lender as a result of its failure to perform its
     obligations under Section 2.

     10.5. Sharing of Payments, etc.  Each Lender agrees that (a) if by
           -------------------------                                   
exercising any right of set-off or counterclaim or otherwise, it shall receive
payment of (i) a proportion of the aggregate amount due with respect to its
Percentage Interest in the Loan and Letter of Credit Exposure which is greater
than (ii) the proportion received by any other Lender in respect of the
aggregate amount due with respect to such other Lender's Percentage Interest in
the Loan and Letter of Credit Exposure and (b) if such inequality shall continue
for more than 10 days, the Lender receiving such proportionately greater payment
shall purchase participations in the Percentage Interests in the Loan and Letter
of Credit Exposure held by the other Lenders, and such other adjustments shall
be made from time to time (including rescission of such purchases of
participations in the event the unequal payment originally received is recovered
from such

                                      -92-
<PAGE>
 
Lender through bankruptcy proceedings or otherwise), as may be required so that
all such payments of principal and interest with respect to the Loan and Letter
of Credit Exposure held by the Lenders shall be shared by the Lenders pro rata
in accordance with their respective Percentage Interests; provided, however,
                                                          --------  -------
that this Section 10.5 shall not impair the right of any Lender to exercise any
right of set-off or counterclaim it may have and to apply the amount subject to
such exercise to the payment of Indebtedness of any Obligor other than such
Obligor's Indebtedness with respect to the Loan and Letter of Credit Exposure.
Each Lender that grants a participation in the Credit Obligations to a Credit
Participant shall require as a condition to the granting of such participation
that such Credit Participant agree to share payments received in respect of the
Credit Obligations as provided in this Section 10.5. The provisions of this
Section 10.5 are for the sole and exclusive benefit of the Lenders and no
failure of any Lender to comply with the terms hereof shall be available to any
Obligor as a defense to the payment of the Credit Obligations.

     10.6. Agent's Resignation.  The Agent may resign at any time by giving at
           -------------------                                                
least 60 days' prior written notice of its intention to do so to each of the
Lenders and the Company and upon the appointment by the Required Lenders of a
successor Agent reasonably satisfactory to the Company.  If no successor Agent
shall have been so appointed and shall have accepted such appointment within 45
days after the retiring Agent's giving of such notice of resignation, then the
retiring Agent may appoint a successor Agent which shall be a bank or a trust
company organized under the laws of the United States of America or any state
thereof and having a combined capital, surplus and undivided profit of at least
$100,000,000 (so long as no Default exists) with the consent of the Company,
which shall not be unreasonably withheld; provided, however, that any successor
                                          --------  -------                    
Agent appointed under this sentence may be removed upon the written request of
the Required Lenders, which request shall also appoint a successor Agent (so
long as no Default exists) reasonably satisfactory to the Company.  Upon the
appointment of a new Agent hereunder, the term "Agent" shall for all purposes of
this Agreement thereafter mean such successor.  After any retiring Agent's
resignation hereunder as Agent, or the removal hereunder of any successor Agent,
the provisions of this Agreement shall continue to inure to the benefit of such
retiring or removed Agent as to any actions taken or omitted to be taken by it
while it was Agent under this Agreement.

     10.7. Concerning the Agent.
           -------------------- 

           10.7.1. Action in Good Faith, etc.  The Agent and its officers,
                   -------------------------                              
     directors, employees and agents shall be under no liability to any of the
     Lenders or to any future holder of any interest in the Credit Obligations
     for any action or failure to act taken or suffered in good faith, and any
     action or failure to act in accordance with an opinion of its counsel shall
     conclusively be deemed to be in good faith. The Agent shall in all cases be
     entitled to rely, and shall be fully protected in relying, on instructions
     given to the Agent by the Required Lenders.

                                      -93-
<PAGE>
 
          10.7.2. No Implied Duties, etc.  The Agent shall have and may exercise
                  ----------------------                                        
such powers as are specifically delegated to the Agent under this Agreement or
any other Credit Document together with all other powers incidental thereto.
The Agent shall have no implied duties to any Person or any obligation to take
any action under this Agreement or any other Credit Document except for action
specifically provided for in this Agreement or any other Credit Document to be
taken by the Agent.

          10.7.3. Validity, etc. The Agent shall not be responsible to any
                  -------------
Lender or any future holder of any interest in the Credit Obligations (a) for
the legality, validity, enforceability or effectiveness of this Agreement or any
other Credit Document, (b) for any recitals, reports, representations,
warranties or statements contained in or made in connection with this Agreement
or any other Credit Document, (c) for the existence or value of any assets
included in any security for the Credit Obligations, (d) for the effectiveness
of any Lien purported to be included in the Credit Security, (e) for the
specification or failure to specify any particular assets to be included in the
Credit Security, or (f) unless the Agent shall have failed to comply with
Section 10.7.1, for the perfection of the security interests in the Credit
Security.

          10.7.4. Compliance.  The Agent shall not be obligated to ascertain or
                  ----------                                                   
inquire as to the performance or observance of any of the terms of this
Agreement or any other Credit Document; and in connection with any extension of
credit under this Agreement or any other Credit Document, the Agent shall be
fully protected in relying on a certificate of the U.S. Borrower or the Canadian
Borrower, as the case may be, as to the fulfillment by the U.S. Borrower or the
Canadian Borrower, as the case may be, of any conditions to such extension of
credit.

          10.7.5. Employment of Agents and Counsel. The Agent may execute any of
                  --------------------------------
its duties as Agent under this Agreement or any other Credit Document by or
through employees, agents and attorneys-in-fact and shall not be responsible to
any of the Lenders, the Borrowers or any other Obligor for the default or
misconduct of any such agents or attorneys-in-fact selected by the Agent acting
in good faith. The Agent shall be entitled to advice of counsel concerning all
matters pertaining to the agency hereby created and its duties hereunder or
under any other Credit Document.

          10.7.6. Reliance on Documents and Counsel. The Agent shall be entitled
                  ---------------------------------
to rely, and shall be fully protected in relying, upon any affidavit,
certificate, cablegram, consent, instrument, letter, notice, order, document,
statement, telecopy, telegram, telex or teletype message or writing reasonably
believed in good faith by the Agent to be genuine and correct and to have been
signed, sent or made by the Person in question, including any telephonic or oral
statement made by such Person, and, with respect to legal matters, upon an
opinion or the advice of counsel selected by the Agent.

                                      -94-
<PAGE>
 
           10.7.7. Agent's Reimbursement. Each of the Lenders severally agrees
                   --------------------- 
     to reimburse the Agent, pro rata in accordance with such Lender's
     Percentage Interest, for any reasonable expenses not reimbursed by the
     Borrowers or the Guarantors (without limiting the obligation of the
     Borrowers or the Guarantors to make such reimbursement): (a) for which the
     Agent is entitled to reimbursement by the Borrowers or the Guarantors under
     this Agreement or any other Credit Document, and (b) after the occurrence
     of a Default, for any other reasonable expenses incurred by the Agent on
     the Lenders' behalf in connection with the enforcement of the Lenders'
     rights under this Agreement or any other Credit Document; provided,
                                                               -------- 
     however, that the Agent shall not be reimbursed for any such expenses
     -------
     arising as a result of its gross negligence or willful misconduct.

     10.8. Rights as a Lender.  With respect to any credit extended by it
           ------------------                                            
hereunder, BankBoston shall have the same rights, obligations and powers
hereunder as any other Lender and may exercise such rights and powers as though
it were not the Agent, and unless the context otherwise specifies, BankBoston
shall be treated in its individual capacity as though it were not the Agent
hereunder.  Without limiting the generality of the foregoing, the Percentage
Interest of BankBoston shall be included in any computations of Percentage
Interests.  BankBoston and its Affiliates may accept deposits from, lend money
to, act as trustee for and generally engage in any kind of banking or trust
business with the Company, any of its Subsidiaries or any Affiliate of any of
them and any Person who may do business with or own an equity interest in the
Company, any of its Subsidiaries or any Affiliate of any of them, all as if
BankBoston were not the Agent and without any duty to account therefor to the
other Lenders.

     10.9  Independent Credit Decision.  Each of the Lenders acknowledges that
           ---------------------------                                        
it has independently and without reliance upon the Agent, based on the financial
statements and other documents referred to in Section 7.2, on the other
representations and warranties contained herein and on such other information
with respect to the Company and its Subsidiaries as such Lender  deemed
appropriate, made such Lender's own credit analysis and decision to enter into
this Agreement and to make the extensions of credit provided for hereunder.
Each Lender represents to the Agent that such Lender will continue to make its
own independent credit and other decisions in taking or not taking action under
this Agreement or any other Credit Document.  Each Lender expressly acknowledges
that neither the Agent nor any of its officers, directors, employees, agents,
attorneys-in-fact or Affiliates has made any representations or warranties to
such Lender, and no act by the Agent taken under this Agreement or any other
Credit Document, including any review of the affairs of the Company and its
Subsidiaries, shall be deemed to constitute any representation or warranty by
the Agent.  Except for notices, reports and other documents expressly required
to be furnished to each Lender by the Agent under this Agreement or any other
Credit Document, the Agent shall not have any duty or responsibility to provide
any Lender with any credit or other information concerning the business,
operations, property, condition, financial or otherwise, or creditworthiness of
the Company or any Subsidiary which may come into the possession of the Agent or
any of its officers, directors, employees, agents, attorneys-in-fact or
Affiliates.

                                      -95-
<PAGE>
 
     10.10.  Indemnification. The Lenders shall severally indemnify the Agent
             ---------------
and its officers, directors, employees, agents, attorneys, accountants,
consultants and controlling Persons (to the extent not reimbursed by the
Obligors and without limiting the obligation of any of the Obligors to do so),
pro rata in accordance with their respective Percentage Interests, from and
against any and all liabilities, obligations, losses, damages, penalties,
actions, judgments, suits, costs, expenses or disbursements of any kind
whatsoever which may at any time be imposed on, incurred by or asserted against
the Agent or such Persons relating to or arising out of this Agreement, any
other Credit Document, the transactions contemplated hereby or thereby, or any
action taken or omitted by the Agent in connection with any of the foregoing;
provided, however, that the foregoing shall not extend to actions or omissions
--------  -------
which are taken by the Agent with gross negligence or willful misconduct.

11.  Successors and Assigns; Lender Assignments and Participations. Any
     -------------------------------------------------------------
reference in this Agreement or any other Credit Document to any of the parties
hereto shall be deemed to include the successors and assigns of such party, and
all covenants and agreements by or on behalf of the Company, the other Obligors,
the Agent or the Lenders that are contained in this Agreement or any other
Credit Document shall bind and inure to the benefit of their respective
successors and assigns; provided, however, that (a) the Company and its
                        --------  -------
Subsidiaries may not assign their rights or obligations under this Agreement or
any other Credit Document except for mergers or liquidations permitted by
Section 6.11, and (b) the Lenders shall be not entitled to assign their
respective Percentage Interests in the credits extended hereunder or their
Commitments except as set forth below in this Section 11.

     11.1. Assignments by Lenders.
           ---------------------- 

           11.1.1.   Assignees and Assignment Procedures.  Each Lender may (a)
                     -----------------------------------                      
     without the consent of the Agent or the Company if the proposed assignee is
     already a Lender hereunder, a Related Fund or a Wholly Owned Subsidiary of
     the same corporate parent of which the assigning Lender or any other Lender
     is a Subsidiary, or (b) otherwise with the consents of the Agent and (so
     long as no Event of Default exists) the Company (which consents will not be
     unreasonably withheld), in compliance with applicable laws in connection
     with such assignment, assign to one or more commercial banks, investment
     companies, other financial institutions or mutual funds in the business of
     making or purchasing loans similar to the Credit Obligations (each, an
     "Assignee") all or a portion of its interests, rights and obligations under
      --------
     this Agreement and the other Credit Documents, including all or a portion,
     which need not be pro rata between the Revolving Loan, Canadian Loan and
     the Letter of Credit Exposure, of its Commitment, the portion of the Loan
     and Letter of Credit Exposure at the time owing to it and any Notes held by
     it, but excluding its rights and obligations as a Letter of Credit Issuer;
     provided, however, that:
     --------  -------

                     (i)   the aggregate amount of the Commitment of the
          assigning Lender subject to each such assignment to any Assignee other
          than another Lender, a

                                      -96-
<PAGE>
 
          Related Fund or a Wholly Owned Subsidiary of the same corporate parent
          of which the assigning Lender or any other Lender is a Subsidiary
          (determined as of the date the Assignment and Acceptance with respect
          to such assignment is delivered to the Agent) shall be not less than
          $2,500,000 and in increments of $1,000,000 (or, if less, the entire
          remaining amount of the assigning Lender's Commitment); and

               (ii)   the parties to each such assignment shall execute and
          deliver to the Agent an Assignment and Acceptance (the "Assignment and
                                                                  --------------
          Acceptance") substantially in the form of Exhibit 11.1.1, together
          ----------
          with the Note subject to such assignment and, except in the event of a
          transfer pursuant to Section 11.3, a processing and recordation fee of
          $3,000 payable to the Agent by the assigning Lender (or as the
          assigning Lender and the Assignee may otherwise agree between
          themselves).

     Upon acceptance and recording pursuant to Section 11.1.4, from and after
     the effective date specified in each Assignment and Acceptance (which
     effective date shall be at least five Banking Days after the execution
     thereof unless waived by the Agent):

          (A)      the Assignee shall be a party hereto and, to the extent
                   provided in such Assignment and Acceptance, have the rights
                   and obligations of a Lender under this Agreement and

          (B)      the assigning Lender shall, to the extent provided in such
                   assignment, be released from its obligations under this
                   Agreement (and, in the case of an Assignment and Acceptance
                   covering all or the remaining portion of an assigning
                   Lender's rights and obligations under this Agreement, such
                   Lender shall cease to be a party hereto but shall continue to
                   be entitled to the benefits of Sections 3.2.4, 3.5 and 9, as
                   well as to any fees accrued for its account hereunder and not
                   yet paid).

          11.1.2.  Terms of Assignment and Acceptance. By executing and
                   ----------------------------------
     delivering an Assignment and Acceptance, the assigning Lender and Assignee
     shall be deemed to confirm to and agree with each other and the other
     parties hereto as follows:

          (a)  other than the representation and warranty that it is the legal
     and beneficial owner of the interest being assigned thereby free and clear
     of any adverse claim, such assigning Lender makes no representation or
     warranty and assumes no responsibility with respect to any statements,
     warranties or representations made in or in connection with this Agreement
     or the execution, legality, validity, enforceability, genuineness,
     sufficiency or value of this Agreement, any other Credit Document or any
     other instrument or document furnished pursuant hereto;

                                      -97-
<PAGE>
 
           (b)   such assigning Lender makes no representation or warranty and
     assumes no responsibility with respect to the financial condition of the
     Company and its Subsidiaries or the performance or observance by the
     Company or any of its Subsidiaries of any of its obligations under this
     Agreement, any other Credit Document or any other instrument or document
     furnished pursuant hereto;

           (c)   such Assignee confirms that it has received a copy of this
     Agreement, together with copies of the most recent financial statements
     delivered pursuant to Section 7.2 or Section 6.4 and such other documents
     and information as it has deemed appropriate to make its own credit
     analysis and decision to enter into such Assignment and Acceptance;

           (d)   such Assignee will independently and without reliance upon the
     Agent, such assigning Lender or any other Lender, and based on such
     documents and information as it shall deem appropriate at the time,
     continue to make its own credit decisions in taking or not taking action
     under this Agreement;

           (e)   such Assignee appoints and authorizes the Agent to take such
     action as agent on its behalf and to exercise such powers under this
     Agreement as are delegated to the Agent by the terms hereof, together with
     such powers as are reasonably incidental thereto; and

           (f)   such Assignee agrees that it will perform in accordance with
     the terms of this Agreement all the obligations which are required to be
     performed by it as a Lender.

           11.1.3.  Register.  The Agent shall maintain at the Boston Office a
                    --------                                                  
register (the "Register") for the recordation of (a) the names and addresses of
               --------                                                        
the Lenders and the Assignees which assume rights and obligations pursuant to an
assignment under Section 11.1.1, (b) the Percentage Interest of each such Lender
as set forth in Exhibit 10.1 and (c) the amount of the Loan and Letter of Credit
Exposure owing to each Lender from time to time.  The entries in the Register
shall be conclusive, in the absence of manifest error, and the Borrowers, the
Agent and the Lenders may treat each Person whose name is registered therein for
all purposes as a party to this Agreement.  The Register shall be available for
inspection by the Borrowers or any Lender at any reasonable time and from time
to time upon reasonable prior notice.

          11.1.4.   Acceptance of Assignment and Assumption. Upon its receipt of
                    ---------------------------------------
a completed Assignment and Acceptance executed by an assigning Lender and an
Assignee (and any necessary consent of the Agent and the Company) together with
the processing and recordation fee referred to in Section 11.1.1 and, to the
extent necessary, the Note being assigned, the Agent shall (a) accept such
Assignment and Acceptance, (b) record the information contained therein in the
Register and (c) give prompt notice thereof to the U.S. Borrower or the Canadian
Borrower, as the case may be. Within five Banking Days

                                      -98-
<PAGE>
 
     after receipt of notice, the U.S. Borrower or the Canadian Borrower, as the
     case may be, at its own expense, shall execute and deliver to the Agent (in
     exchange for the surrendered Note if such Note must be surrendered or
     reissued as a result of such assignment) a new Note to the order of such
     Assignee in a principal amount equal to the applicable Commitment and Loan
     assumed by it pursuant to such Assignment and Acceptance. If the assigning
     Lender has retained a Commitment and Loan, its Note shall be deemed to be
     then outstanding in a principal amount equal to the applicable Commitment
     and Loan retained by it.

           11.1.5. Federal Reserve Bank. Notwithstanding the foregoing
                   --------------------
     provisions of this Section 11 (without the consent of or notice to the
     Agent or the Company), any Lender may at any time pledge all or any portion
     of such Lender's rights under this Agreement and the other Credit Documents
     to a Federal Reserve Bank or, in the case of any Lender that is a fund, to
     the trustee of such fund to support the fund's obligations to such trustee;
     provided, however, that no such pledge or assignment shall release such
     --------  -------
     Lender from such Lender's obligations hereunder or under any other Credit
     Document.

           11.1.6. Further Assurances. The Company and its Subsidiaries shall
                   ------------------
     sign such documents and take such other actions from time to time
     reasonably requested by an Assignee to enable it to share in the benefits
     of the rights created by the Credit Documents.

     11.2. Credit Participants.  Each Lender may, without the consent of the
           -------------------                                              
Company or the Agent, in compliance with applicable laws in connection with such
participation, sell to one or more commercial banks, other financial
institutions or funds in the business of making or purchasing loans similar to
the Credit Obligations (each a "Credit Participant") participations in all or a
                                ------------------                             
portion of its interests, rights and obligations under this Agreement and the
other Credit Documents (including all or a portion of its Commitment, the Loan
and Letter of Credit Exposure owing to it and the Note held by it); provided,
                                                                    -------- 
however, that:
-------       

           (a)   such Lender's obligations under this Agreement shall remain
     unchanged;

           (b)   such Lender shall remain solely responsible to the other
     parties hereto for the performance of such obligations;

           (c)   the Credit Participant shall be entitled to the benefit of the
     cost protection provisions contained in Sections 3.2.4, 3.5 and 9, but
     shall not be entitled to receive any greater payment thereunder than the
     selling Lender would have been entitled to receive with respect to the
     interest so sold if such interest had not been sold; and

           (d)   the U.S. Borrower or the Canadian Borrower, as the case may be,
     the Agent and the other Lenders shall continue to deal solely and directly
     with such Lender in connection with such Lender's rights and obligations
     under this Agreement and, under

                                      -99-
<PAGE>
 
     any agreements between such Lender and such Credit Participant, such Lender
     shall retain the sole right as one of the Lenders to vote (and to determine
     how to vote) with respect to the enforcement of the obligations of the
     Obligors relating to the Loan and Letter of Credit Exposure and the
     approval of any amendment, modification or waiver of any provision of this
     Agreement (other than amendments, modifications, consents or waivers
     described in clause (b) of the proviso to Section 15.1, with respect to
     which the Credit Participant may determine how to vote).

Each Obligor agrees, to the fullest extent permitted by applicable law, that any
Credit Participant and any Lender purchasing a participation from another Lender
pursuant to Section 10.5 may exercise all rights of payment (including the right
of set-off), with respect to its participation as fully as if such Credit
Participant or such Lender were the direct creditor of the Obligors and a Lender
hereunder in the amount of such participation.

     11.3. Replacement of Lender.  In the event that any Lender or, to the
           ---------------------                                          
extent applicable, any Credit Participant (the "Affected Lender"):
                                                ---------------   

           (a)   fails to perform its obligations to fund any portion of the
     Loan or to issue any Letter of Credit on any Closing Date when required to
     do so by the terms of the Credit Documents, or fails to provide its portion
     of any Eurodollar Pricing Option pursuant to Section 3.2.1 or on account of
     a Legal Requirement as contemplated by Section 3.2.5 or, in the case of the
     Canadian Lender, fails to provide any portion of the Canadian Loan pursuant
     to Section 2.3.3;

           (b)   demands payment under the provisions of Section 3.5 in an
     amount materially in excess of the amounts with respect thereto demanded by
     the other Lenders; or

           (c)   refuses to consent to a proposed amendment, modification,
     waiver or other action requiring consent of the holders of 100% of the
     Percentage Interests under Section 15.1 that is consented to by Lenders
     owning at least 90% of the Percentage Interests;

then, so long as no Event of Default exists, the Company shall have the right to
seek a replacement lender which is reasonably satisfactory to the Agent (the
"Replacement Lender"). The Replacement Lender shall purchase the interests of
-------------------                                                          
the Affected Lender in the Loan, Letters of Credit and its Commitment and shall
assume the obligations of the Affected Lender hereunder and under the other
Credit Documents upon execution by the Replacement Lender of an Assignment and
Acceptance and the tender by it to the Affected Lender of a purchase price
agreed between it and the Affected Lender (or, if they are unable to agree, a
purchase price in the amount of the Affected Lender's Percentage Interest in the
Loan and Letter of Credit Exposure, or appropriate credit support for contingent
amounts included therein, and all other outstanding Credit Obligations then owed
to the Affected Lender).  No assignment fee pursuant to Section 11.1.1(ii) shall
be required in connection with such assignment.  Such assignment by any

                                     -100-
<PAGE>
 
Affected Lender who has performed its obligations hereunder shall be deemed an
early termination of any Eurodollar Pricing Option to the extent of such
Affected Lender's portion thereof, and the U.S. Borrower will pay to such
Affected Lender any resulting amounts due under Section 3.2.4. Upon consummation
of such assignment, the Replacement Lender shall become party to this Agreement
as a signatory hereto and shall have all the rights and obligations of the
Affected Lender under this Agreement and the other Credit Documents with a
Percentage Interest equal to the Percentage Interest of the Affected Lender, the
Affected Lender shall be released from its obligations hereunder and under the
other Credit Documents, and no further consent or action by any party shall be
required. Upon the consummation of such assignment, the U.S. Borrower or the
Canadian Borrower, as the case may be, the Agent and the Affected Lender shall
make appropriate arrangements so that a new Note is issued to the Replacement
Lender if it has acquired a portion of the Loan. The U.S. Borrower or the
Canadian Borrower, as the case may be, and the Guarantors shall sign such
documents and take such other actions reasonably requested by the Replacement
Lender to enable it to share in the benefits of the rights created by the Credit
Documents. Until the consummation of an assignment in accordance with the
foregoing provisions of this Section 11.3, the U.S. Borrower or the Canadian
Borrower, as the case may be, shall continue to pay to the Affected Lender any
Credit Obligations as they become due and payable.

12.  Confidentiality.  Each Lender will make no disclosure of confidential
     ---------------                                                      
information furnished to it by the Company or any of its Subsidiaries unless
such information shall have become public, except:

           (a)   in connection with operations under or the enforcement of this
     Agreement or any other Credit Document to Persons who have a reasonable
     need to be furnished such confidential information and who agree to comply
     with the restrictions contained in this Section 12 with respect to such
     information;

           (b)   pursuant to any statutory or regulatory requirement or any
     mandatory court order, subpoena or other legal process;

           (c)   to any parent or corporate Affiliate of such Lender or to any
     Credit Participant, proposed Credit Participant or proposed Assignee;
     provided, however, that any such Person shall agree to comply with the
     --------  -------                                                     
     restrictions set forth in this Section 12 with respect to such information;

           (d)   to its independent counsel, auditors and other professional
     advisors with an instruction to such Person to keep such information
     confidential; and

           (e)   with the prior written consent of the Company, to any other
     Person.

13.  Foreign Lenders.  If any Lender (other than the Canadian Lender) is not
     ---------------                                                        
created or organized in, or under the laws of, the United States of America or
any state thereof, such Lender 

                                     -101-
<PAGE>
 
shall deliver to the U.S. Borrower or the Canadian Borrower, as the case may be,
and the Agent the forms described in one of the following two clauses (or the
equivalent thereof required under Canadian law):

           (a)  Two fully completed and duly executed United States Internal
     Revenue Service Form 1001 or 4224 or any successor form, as the case may
     be, certifying that such Lender is entitled to receive payments of the
     Credit Obligations payable to it without deduction or withholding of any
     United States federal income taxes; or

           (b)  A statement, executed by such Lender under penalty of perjury,
     certifying that such Lender is not a "bank" within the meaning of section
     881(c)(3)(A) of the Code and two fully completed and duly executed United
     States Internal Revenue Service Forms W-8 or any successor form, certifying
     that such Lender is not a "United States person" within the meaning of
     section 7701(a)(30) of the Code.
 
Each Lender that delivers any form or statement pursuant to this Section 13
further undertakes to renew such forms and statements by delivering to the U.S.
Borrower or the Canadian Borrower, as the case may be, and the Agent any updated
form, successor form or other certification, as the case may be, on or before
the date that any form or statement previously delivered pursuant to this
Section 13 expires or becomes obsolete or after the occurrence of any event
requiring a change in such most recent form or statement.  If at any time the
U.S. Borrower or the Canadian Borrower, as the case may be, and the Agent have
not received all forms and statements (including any renewals thereof) required
to be provided by any Lender pursuant to this Section 13, Section 3.5 shall not
apply with respect to any amount of  United States federal income taxes required
to be withheld from payments of the Credit Obligations to such Lender.

14.  Notices.  Except as otherwise specified in this Agreement or any other
     -------                                                               
Credit Document, any notice required to be given pursuant to this Agreement or
any other Credit Document shall be given in writing.  Any notice, consent,
approval, demand or other communication in connection with this Agreement or any
other Credit Document shall be deemed to be given if given in writing (including
telex, telecopy or similar teletransmission) addressed as provided below (or to
the addressee at such other address as the addressee shall have specified by
notice actually received by the addressor), and if either (a) actually delivered
in fully legible form to such address (evidenced in the case of a telex by
receipt of the correct answer back) or (b) in the case of a letter, unless
actual receipt of the notice is required by any Credit Document five days shall
have elapsed after the same shall have been deposited in the United States
mails, with first-class postage prepaid and registered or certified.

     If to the Company or any of its Subsidiaries, to it at its address set
forth in Exhibit 7.1 (as supplemented pursuant to Sections 6.4.1 and 6.4.2), to
the attention of the chief financial officer.

     If to any Lender or the Agent, to it at its address set forth on the
signature pages of this Agreement or in the Register, with a copy to the Agent.

                                     -102-
<PAGE>
 
15.  Amendments, Consents, Waivers, etc.
     ---------------------------------- 

     15.1  Lender Consents for Amendments.  Except as otherwise set forth
           ------------------------------                                
herein, the Agent may (and upon the written request of the Required Lenders the
Agent shall) take or refrain from taking any action under this Agreement or any
other Credit Document, including giving its written consent to any modification
of or amendment to and waiving in writing compliance with any covenant or
condition in this Agreement or any other Credit Document (other than an Interest
Rate Protection Agreement) or any Default or Event of Default, all of which
actions shall be binding upon all of the Lenders; provided, however, that:
                                                  --------  -------       

           (a)   Except as provided below, without the written consent of the
     Lenders owning at least two-thirds of the Percentage Interests
     (disregarding the Percentage Interest of any Delinquent Lender during the
     existence of a Delinquency Period or of any Nonperforming Lender so long as
     such Lender is treated equally with the other Lenders with respect to any
     actions enumerated below), no written modification of, amendment to,
     consent with respect to, waiver of compliance with or waiver of a Default
     under, any of the Credit Documents (other than an Interest Rate Protection
     Agreement) shall be made.

           (b)   Without the written consent of such Lenders as own 100% of the
     Percentage Interests (disregarding the Percentage Interest of any
     Delinquent Lender during the existence of a Delinquency Period or of any
     Nonperforming Lender so long as such Lender is treated equally with the
     other Lenders with respect to any actions enumerated below):

               (i)     None of the conditions specified in Section 5 shall be
          amended, waived or modified.

               (ii)    No release of all or substantially all of the Credit
          Security or release of either Borrower or any material Guarantor shall
          be made (in any event, without the written consent of the Lenders, the
          Agent may release particular items of Credit Security or particular
          Guarantors in dispositions permitted by Section 6.11, as modified by
          amendments thereto approved by the Required Lenders, and may release
          all Credit Security pursuant to Section 16.1 upon payment in full of
          the Credit Obligations and termination of the Commitments).

               (iii)   No incurrence or existence of any Lien on all or
          substantially all of the Credit Security shall be permitted (other
          than Liens securing the Credit Obligations).

               (iv)    No alteration shall be made of the Lenders' rights of 
          set-off contained in Section 8.2.4.

                                     -103-
<PAGE>
 
               (v)     No amendment to or modification of this Section 15.1 or
          the definition of "Required Lenders" shall be made.

          (c)  Without the written consent of each Lender that is directly
     affected thereby, together with such Lenders as own at least a majority of
     the Percentage Interests (disregarding the Percentage Interest of any
     Delinquent Lender during the existence of a Delinquency Period or of any
     Nonperforming Lender so long as such Lender is treated equally with the
     other Lenders with respect to any actions enumerated below):

               (i)     No reduction shall be made in (A) the amount of principal
          of the Loan owing to such Lender or reimbursement obligations for
          payments made under Letters of Credit payable or participated to such
          Lender, (B) the interest rate on the portion of the Loan owing to such
          Lender or (C) the Letter of Credit fees or commitment fees owing to
          such Lender with respect to the credit facility provided herein (other
          than amendments and waivers approved by the Required Lenders that
          modify defined terms used in calculating the Applicable Margin or
          Consolidated Excess Cash Flow or that waive an increase in the
          Applicable Rate as a result of an Event of Default).

               (ii)    No change shall be made in the stated, scheduled time of
          payment of  any portion of the Loan owing to such Lender or interest
          thereon or reimbursement of payments made under Letters of Credit or
          fees relating to any of the foregoing payable to such Lender and no
          waiver shall be made of any Default under Section 8.1.1 with respect
          to such Lender (other than amendments and waivers approved by the
          Required Lenders that modify defined terms used in calculating the
          Applicable Margin or Consolidated Excess Cash Flow).

               (iii)   No increase shall be made in the amount, or extension of
          the term, of the stated Commitments of such Lender beyond that
          provided for under Section 2.

          (d)  Without the written consent of such Lenders owning at least a
     majority of the Percentage Interests in a particular Tranche (disregarding
     the Percentage Interest of any Delinquent Lender during the existence of a
     Delinquency Period or of any Nonperforming Lender so long as such Lender is
     treated equally with the other Lenders with respect to any actions
     enumerated below) voting as a separate class, no change may be made in the
     allocation of mandatory prepayments under Section 4.2 between the
     respective Tranches.

          (e)  Without the written consent of the Agent, no amendment or
     modification of any Credit Document shall affect the rights or duties of
     the Agent under the Credit Documents.

                                     -104-
<PAGE>
 
           (f)   Without the written consent of a Letter of Credit Issuer, no
     amendment or modification of any Credit Document shall affect the rights or
     duties of such Letter of Credit Issuer under the Credit Documents.

           (g)   Without the written consent of the Canadian Lender, no
     amendment or modification of any Credit Document shall affect the rights or
     duties of the Canadian Lender under the Credit Documents.

     15.2. Course of Dealing; No Implied Waivers.  No course of dealing between
           -------------------------------------                               
any Lender or the Agent, on one hand, and either of  the Borrowers or any other
Obligor, on the other hand, shall operate as a waiver of any of the Lenders' or
the Agent's rights under this Agreement or any other Credit Document or with
respect to the Credit Obligations.  In particular, no delay or omission on the
part of any Lender or the Agent in exercising any right under this Agreement or
any other Credit Document or with respect to the Credit Obligations shall
operate as a waiver of such right or any other right hereunder or thereunder.  A
waiver on any one occasion shall not be construed as a bar to or waiver of any
right or remedy on any future occasion.  No waiver, consent or amendment with
respect to this Agreement or any other Credit Document shall be binding unless
it is in writing and signed by the Agent or the Required Lenders.

16.  General Provisions.
     ------------------ 

     16.1. Defeasance.  When all Credit Obligations have been paid, performed
           ----------                                                        
and reasonably determined by the Agent to have been discharged in full, and if
at the time no Lender continues to be committed to extend any credit to the
Company hereunder or under any other Credit Document, this Agreement and the
other Credit Documents shall terminate and, at the Company's written request,
accompanied by such certificates and other items as the Agent shall reasonably
deem necessary, the Credit Security shall revert to the Obligors and the right,
title and interest of the Agent and the Lenders therein shall terminate.
Thereupon, on the Obligors' demand and at their cost and expense, the Agent
shall execute proper instruments, acknowledging satisfaction of and discharging
this Agreement and the other Credit Documents, and shall redeliver to the
Obligors any Credit Security then in its possession; provided, however, that
                                                     --------  -------      
Sections 3.2.4, 3.5, 9, 10.7.7, 10.10, 12 and 16 shall survive the termination
of this Agreement.

     16.2. No Strict Construction.  The parties have participated jointly in the
           ----------------------                                               
negotiation and drafting of this Agreement and the other Credit Documents with
counsel sophisticated in financing transactions.  In the event an ambiguity or
question of intent or interpretation arises, this Agreement and the other Credit
Documents shall be construed as if drafted jointly by the parties and no
presumption or burden of proof shall arise favoring or disfavoring any party by
virtue of the authorship of any provisions of this Agreement and the other
Credit Documents.

                                     -105-
<PAGE>
 
     16.3. Certain Obligor Acknowledgments.  Each of the Borrowers and the other
           -------------------------------                                      
Obligors acknowledges that:

           (a)   it has been advised by counsel in the negotiation, execution
     and delivery of this Agreement and the other Credit Documents;

           (b)   neither the Agent nor any Lender has any fiduciary relationship
     with or duty to the Obligors arising out of or in connection with this
     Agreement or any other Credit Document, and the relationship between the
     Agent and Lenders, on one hand, and the Obligors, on the other hand, in
     connection herewith or therewith is solely that of debtor and creditor; and

           (c)   no joint venture is created hereby or by the other Credit
     Documents or otherwise exists by virtue of the transactions contemplated
     hereby or thereby among the Obligors and the Lenders.

     16.4. Venue; Service of Process; Certain Waivers.  Each of the Borrowers,
           ------------------------------------------                         
the other Obligors, the Agent and the Lenders:

           (a)   Irrevocably submits to the nonexclusive jurisdiction of the
     state courts of The Commonwealth of Massachusetts and to the nonexclusive
     jurisdiction of the United States District Court for the District of
     Massachusetts for the purpose of any suit, action or other proceeding
     arising out of or based upon this Agreement or any other Credit Document or
     the subject matter hereof or thereof;

           (b)   Waives to the extent not prohibited by applicable law that
     cannot be waived, and agrees not to assert, by way of motion, as a defense
     or otherwise, in any such proceeding brought in any of the above-named
     courts, any claim that it is not subject personally to the jurisdiction of
     such court, that its property is exempt or immune from attachment or
     execution, that such proceeding is brought in an inconvenient forum, that
     the venue of such proceeding is improper, or that this Agreement or any
     other Credit Document, or the subject matter hereof or thereof, may not be
     enforced in or by such court;

           (c)   Consents to service of process in any such proceeding in any
     manner at the time permitted by Chapter 223A of the General Laws of The
     Commonwealth of Massachusetts and agrees that service of process by
     registered or certified mail, return receipt requested, at its address
     specified in or pursuant to Section 14 is reasonably calculated to give
     actual notice; and

           (d)   Waives to the extent not prohibited by applicable law that
     cannot be waived any right it may have to claim or recover in any such
     proceeding any special, exemplary, punitive or consequential damages.

                                     -106-
<PAGE>
 
     16.5. WAIVER OF JURY TRIAL.  TO THE EXTENT NOT PROHIBITED BY APPLICABLE LAW
           --------------------                                                 
THAT CANNOT BE WAIVED, EACH OF THE BORROWERS, THE OTHER OBLIGORS, THE AGENT AND
THE LENDERS WAIVES, AND COVENANTS THAT IT WILL NOT ASSERT (WHETHER AS PLAINTIFF,
DEFENDANT OR OTHERWISE), ANY RIGHT TO TRIAL BY JURY IN ANY FORUM IN RESPECT OF
ANY ISSUE, CLAIM OR PROCEEDING ARISING OUT OF THIS AGREEMENT OR ANY OTHER CREDIT
DOCUMENT OR THE SUBJECT MATTER HEREOF OR THEREOF OR ANY CREDIT OBLIGATION OR IN
ANY WAY CONNECTED WITH THE DEALINGS OF THE LENDERS, THE AGENT, THE BORROWERS OR
ANY OTHER OBLIGOR IN CONNECTION WITH ANY OF THE ABOVE, IN EACH CASE WHETHER NOW
EXISTING OR HEREAFTER ARISING AND WHETHER IN CONTRACT, TORT OR OTHERWISE.  Each
of the Borrowers and the other Obligors acknowledges that it has been informed
by the Agent that the foregoing sentence constitutes a material inducement upon
which each of the Lenders has relied and will rely in entering into this
Agreement and any other Credit Document.  Any Lender, the Agent, the Borrowers
or any other Obligor may file an original counterpart or a copy of this
Agreement with any court as written evidence of the consent of the Borrowers,
the other Obligors, the Agent and the Lenders to the waiver of their rights to
trial by jury.

     16.6. Interpretation; Governing Law; etc.  Time is (and shall be) of the
           ----------------------------------                                
essence in this Agreement and the other Credit Documents.  All covenants,
agreements, representations and warranties made in this Agreement or any other
Credit Document or in certificates delivered pursuant hereto or thereto shall be
deemed to have been relied on by each Lender, notwithstanding any investigation
made by any Lender on its behalf, and shall survive the execution and delivery
to the Lenders hereof and thereof.  The invalidity or unenforceability of any
provision hereof shall not affect the validity or enforceability of any other
provision hereof, and any invalid or unenforceable provision shall be modified
so as to be enforced to the maximum extent of its validity or enforceability.
The headings in this Agreement are for convenience of reference only and shall
not limit or otherwise affect the meaning hereof.  This Agreement and the other
Credit Documents constitute the entire understanding of the parties with respect
to the subject matter hereof and thereof and supersede all prior and
contemporaneous understandings and agreements, whether written or oral.  This
Agreement may be executed in any number of counterparts which together shall
constitute one instrument.  This Agreement shall be governed by and construed in
accordance with the laws (other than the conflict of laws rules) of The
Commonwealth of Massachusetts.

                [THE REST OF THIS PAGE IS INTENTIONALLY BLANK.]

                                     -107-
<PAGE>
 
     Each of the undersigned has caused this Agreement to be executed and
delivered by its duly authorized officer as an agreement under seal as of the
date first above written.

                         WESTOWER CORPORATION


                         By /s/ Peter Lucas
                            --------------------------------------    
                            Title: Chief Financial Officer


                         WESTOWER HOLDINGS LTD.


                         By /s/ Peter Lucas
                            --------------------------------------
                            Title: Secretary


                         WESTOWER COMMUNICATIONS LTD.


                         By /s/ Peter Lucas
                            -------------------------------------- 
                            Title: Chief Financial Officer


                         MJA COMMUNICATIONS CORP.


                         By /s/ Peter Lucas
                            -------------------------------------- 
                            Title: Secretary
   

                         NATIONAL TOWER SERVICE LTD.


                         By /s/ Peter Lucas
                            -------------------------------------- 
                            Title: Chief Financial Officer
    

                         RALPH'S RADIO INC.


                         By /s/ Peter Lucas
                            -------------------------------------- 
                            Title: Chief Financial Officer
   
                                     -108-
<PAGE>
 
                         344813 ALBERTA LTD.


                         By /s/ Peter Lucas
                            --------------------------------------            
                            Title: Chief Financial Officer


                         WESTERN TELECOM CONSTRUCTION LTD


                         By /s/ Peter Lucas
                            --------------------------------------            
                            Title: Chief Financial Officer

                         WESTOWER COMMUNICATIONS INC.


                         By /s/ Peter Lucas
                            --------------------------------------            
                            Title: Chief Financial Officer

                         WESTOWER LEASING CANADA INC.


                         By /s/ Peter Lucas
                            --------------------------------------            
                            Title: Chief Financial Officer

                         WTC HOLDINGS INC.


                         By /s/ Peter Lucas
                            --------------------------------------            
                            Title: Chief Financial Officer   

                         WTC LEASING LTD. PARTNERSHIP
                         By 582570 ALBERTA LTD., its general partner


                         By /s/ Peter Lucas
                            --------------------------------------            
                            Title: Chief Financial Officer

                                     -109-
<PAGE>
 
                         3479021 CANADA INC.


                         By /s/ Peter Lucas
                            --------------------------------
                            Title: Chief Financial Officer

                                     -110-
<PAGE>
 
                         BANKBOSTON, N.A.


                         By /s/ Lenny Mason
                            -------------------------------
                            Title: Vice President

                            BANKBOSTON, N.A.
                            Media & Communications Division
                            100 Federal Street
                            Boston, Massachusetts  02110
                            Telecopy: (617) 434-3401
                            Telex:  940581


                         PARIBAS


                         By /s/ Salo Aizendero
                            -------------------------------
                            Title: Vice President


                         By /s/ William B. Schink
                            -------------------------------
                            Title: Director

                            PARIBAS
                            787 Seventh Avenue
                            New York, NY  10019


                         PARIBAS BANK OF CANADA


                         By /s/ James Goodall
                            -------------------------------
                            Title: Managing Director


                         By /s/ William R. Jeffrey
                            -------------------------------
                            Title: Director

                            PARIBAS BANK OF CANADA
                            Royal Trust Tower
                            Suite 4100
                            TD Center
                            Toronto, Ontario  M5K 1N8

 

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<PAGE>
 
                         FLEET NATIONAL BANK


                         By /s/ Tanya M. Crossley
                            -------------------------------------
                            Title: Vice President

                            FLEET NATIONAL BANK
                            1185 Avenue of the Americas, 16th Floor
                            New York, NY  10036


                         U.S. BANK NATIONAL ASSOCIATION


                         By Thomas G. Gunder
                            -------------------------------------
                            Title: Vice President

                            U.S. BANK NATIONAL ASSOCIATION
                            1420 5th Avenue, 10th Floor
                            Seattle, WA  98101


                         UNION BANK OF CALIFORNIA, N.A.


                         By /s/ Michael K. McShane
                            -------------------------------------
                            Title: Senior Vice President

                            UNION BANK OF CALIFORNIA, N.A.
                            445 Figueroa Street, 15th Floor
                            Los Angeles, CA  90071
 

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