<PAGE>   1
                                                                  Exhibit 10.18a



                      SECOND AMENDMENT TO CREDIT AGREEMENT


                  THIS SECOND AMENDMENT TO CREDIT AGREEMENT is dated as of April
8, 1998 (this "SECOND AMENDMENT"), is entered into by and among SYGNET
COMMUNICATIONS, INC., an Ohio corporation (the "BORROWER"), the Lenders which
are parties to the Credit Agreement referred to below (collectively the
"LENDERS"), TORONTO DOMINION (TEXAS), INC. as the Administrative Agent and PNC
BANK, NATIONAL ASSOCIATION as the Documentation Agent and as the Collateral
Agent, and amends the Credit Agreement dated as of October 9, 1996, as
previously amended by that certain Consent, Waiver and Amendment dated March 28,
1997 (the foregoing herein referred to collectively as the "ORIGINAL CREDIT
AGREEMENT"), entered into by and among the Borrower, the Lenders and the Agents
(as that term is defined in the Original Credit Agreement).


                                   WITNESSETH:

                  WHEREAS, the Borrower and the Lenders have agreed to make
certain changes to the interest rates set forth in the Original Credit
Agreement, to provide for a swing line in the principal amount of $5,000,000 to
be made available by PNC Bank, National Association, and to make certain other
changes to the Original Credit Agreement, upon the terms and conditions set
forth herein.

                  NOW THEREFORE, in consideration of the premises, the mutual
covenants and agreements contained herein and other valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, and with the intent to
be legally bound hereby, the parties hereto agree as follows:


                                    ARTICLE I

                     AMENDMENTS TO ORIGINAL CREDIT AGREEMENT
                     ---------------------------------------

                  SECTION 1.01 AMENDMENT TO SECTION 1.1 OF THE ORIGINAL CREDIT
AGREEMENT. Section 1.1 of the Original Credit Agreement is hereby amended as
follows:

                  (a) The following defined terms and the definitions therefor
are added to Section 1.1 in appropriate alphabetical order:

                                    FIRST AMENDMENT: The Consent, Waiver and
                  Amendment dated March 28, 1997 entered into by and between the
                  Borrower and the Documentation Agent, for and on behalf of the
                  Lenders.

                                    PNC BANK: PNC Bank, National Association,
                  and its successors and assigns.


<PAGE>   2

                                    RATABLE SHARE: The proportion that a
                  Lender's Commitment bears to the Commitments of all the
                  Lenders.

                                    SECOND AMENDMENT: The Second Amendment to
                  Credit Agreement dated as of April 8, 1998 entered into by and
                  among the Borrower, the Lenders and the Agents.

                                    SWING LOAN: Any loan made by PNC Bank to the
                  Borrower pursuant to Section 2.1a(ii) hereof.

                                    SWING LOAN COMMITMENT: PNC Bank's commitment
                  to make Swing Loans to the Borrower pursuant to Section
                  2.1a(ii) hereof in an aggregate Dollar amount not to exceed at
                  any one time outstanding $5,000,000.

                                    SWING LOAN NOTE: The Swing Loan Note of the
                  Borrower in the form of Exhibit "A" to the Second Amendment
                  evidencing the Swing Loans, together with all extensions,
                  renewals, amendments, substitutions and replacements thereto
                  and thereof.

                                    SWING LOAN RATE: For any day, a floating
                  rate of interest per annum equal to the sum of (i) the Federal
                  Funds Rate on the day a Swing Loan is requested by the
                  Borrower, plus (ii) (A) the Applicable Margin then in effect
                  with respect to Euro-Rate Loans less (B) the Commitment Fee
                  then in effect pursuant to Section 2.7a. For purposes of this
                  definition only, (i) "Federal Funds Rate" shall mean, for any
                  day, (A) the interest rate per annum (rounded upward, if
                  necessary, to the nearest 1/100 of 1%) determined by PNC Bank
                  (such determination shall be conclusive absent manifest error)
                  to be equal to the weighted average of rates on federal funds
                  transactions among members of the Federal Reserve System
                  arranged by Federal funds brokers at or about 9:00 a.m.
                  (Eastern time) on such day; provided, however, that if such
                  day is not a Business Day, the Federal Funds Rate for such day
                  shall be such rate for such transactions on the immediately
                  preceding Business Day or (B) if no such rates shall be quoted
                  by Federal funds brokers at such time, such other rate as
                  determined by PNC Bank in accordance with its usual procedures
                  (such determination shall be conclusive absent manifest
                  error), and (ii) "Business Day" shall mean any day other than
                  a Saturday or Sunday or a legal holiday on which commercial
                  banks are authorized or required to be closed for business in
                  Philadelphia, Pennsylvania.


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<PAGE>   3

                                    SWING LOAN REQUEST: A request for Swing
                  Loans made in accordance with Section 2.4b hereof.


                  (b) The definitions of the following defined terms are hereby
amended and restated to read as follows:

                                    LOAN: An individual borrowing by the
                  Borrower under the Revolving Credit Commitment or any Swing
                  Loan.

                                    LOAN DOCUMENT: Any of this Agreement, any
                  Revolving Credit Note, the Swing Line Note, any Security
                  Document, any Subsidiary Guaranty Agreement, any Fee Letter,
                  any Interest Hedge Agreement entered into with a Lender, the
                  Management Agreement and all other agreements, documents and
                  instruments executed and delivered to govern, evidence or
                  secure the Obligations, and the statements, reports,
                  certificates and other documents required by, or related to,
                  any of the foregoing, together with all extensions, renewals,
                  amendments, substitutions and replacements to and of any of
                  the foregoing.

                                    OBLIGATIONS: Collectively, (i) all unpaid
                  principal and accrued and unpaid interest (including, without
                  limitation, any interest accruing subsequent to the
                  commencement of a bankruptcy, insolvency or similar proceeding
                  with respect to the Borrower, whether or not such interest
                  constitutes an allowed claim in such proceeding) under the
                  Loans and the Swing Loans, (ii) all accrued and unpaid Fees,
                  (iii) any other amounts due hereunder or under any of the
                  other Loan Documents, including all reimbursements,
                  indemnities, Fees, costs, expenses, prepayment premiums,
                  break-funding costs and other obligations of the Borrower, any
                  Subsidiary of the Borrower or Wireless to any Agent, any
                  Lender or any indemnified party hereunder and thereunder, (iv)
                  any obligations owed by the Borrower to any Lender or to any
                  Affiliate of any Lender pursuant to an Interest Hedge
                  Agreement and (v) all out-of-pocket costs and expenses
                  incurred by the Agents and the Lenders in connection with this
                  Agreement and the other Loan Documents, including but not
                  limited to the reasonable fees and expenses of the Agents'
                  counsel, which the Borrower is responsible to pay pursuant to
                  the terms of this Agreement and the other Loan Documents.

                                    REQUIRED LENDERS: Prior to the termination
                  of the Revolving Credit Commitment, the Lenders whose
                  Commitment 


                                      -3-
<PAGE>   4

                  Percentages aggregate at least sixty-six and two-thirds
                  percent (66 2/3%) of the aggregate Commitment Percentages of
                  all the Lenders, and after the termination of the Revolving
                  Credit Commitment, whether on the stated Maturity Date, by
                  acceleration or otherwise, the Lenders whose outstanding
                  principal amounts of the Loans (including Swing Loans)
                  aggregate at least sixty-six and two-thirds (66 2/3%) of the
                  aggregate principal amount of the outstanding Loans.


                  SECTION 1.02 AMENDMENTS TO SECTION 2.1 OF THE ORIGINAL CREDIT
                  AGREEMENT.

                  (a) The heading of Section 2.1 is hereby amended and restated
to read as follows:

                  2.1 REVOLVING CREDIT COMMITMENT; SWING LOAN COMMITMENT.


                  (b) Subsection 2.1a is hereby amended and restated to read as
follows:

                  2.1a LOANS.

                                    (i) REVOLVING CREDIT LOANS. The Lenders
                  agree, subject to the terms and conditions hereof and relying
                  upon the representations and warranties herein set forth, that
                  the Borrower shall have the right to borrow, repay and
                  reborrow, from the date hereof until the Maturity Date, a
                  principal amount not to exceed in the aggregate the Revolving
                  Credit Commitment at any one time outstanding.

                                    (ii) SWING LOAN COMMITMENT. Subject to the
                  terms and conditions hereof and relying upon the
                  representations and warranties herein set forth, PNC Bank may,
                  at its option, cancelable at any time for any reason
                  whatsoever, make Swing Loans to the Borrower at any time or
                  from time to time to, but not including, the Maturity Date, in
                  an aggregate principal amount not to exceed at any one time
                  $5,000,000; provided that (A) the sum of the aggregate
                  principal amount of PNC Bank's Swing Loans and the Loans of
                  PNC Bank outstanding under the Revolving Credit Commitment
                  shall not exceed at any time PNC Bank's Commitment, and (B)
                  the aggregate principal amount of PNC Bank's Swing Loans and
                  the Loans of all the Lenders at any one time outstanding shall
                  not exceed the Revolving Credit Commitments of all the
                  Lenders. Within such limits of time and 


                                      -4-
<PAGE>   5

                  amount and subject to the other provisions of this Agreement,
                  the Borrower may borrow, repay and reborrow pursuant to this
                  Section 2.1a(ii).

                  (c) Subsection 2.1d is hereby amended and restated in its
entirety to read as follows:

                  2.1d AMOUNT OF LOANS AND REPAYMENTS. Each Base Rate Loan shall
                  be in a minimum amount of $1,000,000, or if in excess of
                  $1,000,000, in integral multiples of $100,000. Each Euro-Rate
                  Loan shall be in a minimum amount of $1,000,000, or if in
                  excess of $1,000,000, in integral multiples of $500,000. Each
                  repayment of a Loan (except for repayments relating to
                  mandatory or voluntary reductions of the Revolving Credit
                  Commitment described in Section 2.1c and repayments due on the
                  Maturity Date) shall be in a minimum amount of $1,000,000.
                  Subject to the other terms and provisions hereof relating to
                  Swing Loans, Swing Loans and repayments of Swing Loans may be
                  in any amount.

                  (d) Subsection 2.1e is hereby amended and restated in its
entirety to read as follows:

                  2.1e REPAYMENT ON MATURITY DATE. On the Maturity Date the
                  entire outstanding principal balance of the Loans and the
                  Swing Loans, plus all accrued and unpaid interest thereon, any
                  unpaid Fees relating thereto and any other outstanding
                  Obligations shall be due and payable, in immediately available
                  funds.

                  (e) Subsection 2.1f is hereby amended and restated in its
entirety to read as follows:

                  2.1f NOTES. The obligations of the Borrower to repay, on or
                  before the Maturity Date, the aggregate unpaid principal
                  amount of the Loans shall be evidenced by Revolving Credit
                  Notes, each substantially in the form of EXHIBIT "A", (i)
                  drawn by the Borrower to the order of a Lender in the maximum
                  amount of that Lender's Commitment Percentage of the
                  Revolving Credit Commitment, (ii) duly executed by the
                  Borrower and (iii) delivered to the Administrative Agent for
                  redelivery to such Lender. The obligation of the Borrower to
                  repay, on or before the Maturity Date, the aggregate unpaid
                  principal amount of the Swing Loans shall be evidenced by the
                  Swing Loan Note substantially in the form of EXHIBIT "A" to
                  the Second Amendment, (i) drawn by the  Borrower to the order 
                  of PNC Bank in the maximum amount of PNC Bank's Swing Loan
                  Commitment, (ii) duly executed by the



                                      -5-
<PAGE>   6

                  Borrower and (iii) delivered to PNC Bank. The principal amount
                  actually due and owing each Lender under the Revolving Credit
                  Note payable to it shall be the aggregate unpaid principal
                  amount of all Loans made by such Lender, and the principal
                  amount actually due and owing PNC Bank under the Swing Loan
                  Note payable to it shall be the aggregate unpaid principal
                  amount of all Swing Loans made by PNC Bank, all as shown on
                  the Loan Accounts established pursuant to Section 2.6.


                  (f) The following new Subsection 2.1g is hereby added to the
Original Credit Agreement, immediately following subsection 2.1f:

                  2.1g OTHER PROVISIONS RELATING TO SWING LOANS.

                                    (i) PNC Bank may, at its option, exercisable
                  at any time for any reason whatsoever, demand repayment of the
                  Swing Loans, and each Lender shall make a Loan in an amount
                  equal to such Lender's Ratable Share of the aggregate
                  principal amount of the outstanding Swing Loans, plus, if PNC
                  Bank so requests, accrued interest thereon; PROVIDED that no
                  Lender shall be obligated in any event to make Loans in excess
                  of its Commitment, and PROVIDED, FURTHER, that PNC Bank may
                  not demand repayment of any Swing Loan, and the Lenders shall
                  not be required to make Loans equal to their respective
                  Ratable Shares of such Swing Loan, if, at the time such Swing
                  Loan was originally made by PNC Bank, PNC Bank had actual
                  knowledge that any of the conditions to lending contained in
                  Subsections 7.1b, 7.1c and 7.1d hereof had not been met. Loans
                  made by the Lenders pursuant to the preceding sentence shall
                  initially bear interest at the Base Rate Option (unless and
                  until converted to another Interest Rate Option hereunder) and
                  shall be deemed to have been properly requested in accordance
                  with Section 2.4(a) without regard to any of the requirements
                  of that provision. PNC Bank shall provide notice to the
                  Administrative Agent (which may be telephonic or written
                  notice by letter, facsimile or telex) that such Loans are to
                  be made under this Subsection 2.1g. Upon receipt of such
                  notice, the Administrative Agent shall provide prompt notice
                  to the Lenders (which may be telephonic or written notice by
                  letter, facsimile or telex) that such Loans are to be made
                  under this Subsection 2.1g, and of the apportionment among the
                  Lenders, and the Lenders shall be unconditionally obligated to
                  fund such Loans (whether or not the conditions specified in
                  Section 2.4(a) are then satisfied) by the time and on the day
                  PNC Bank so requests, which shall not be earlier than 3:00
                  p.m. Eastern time on the Business Day next after 


                                      -6-
<PAGE>   7

                  the date the Lenders receive such notice from the
                  Administrative Agent.

                                    (ii) If at any time the aggregate
                  outstanding principal amount of Loans made by PNC Bank under
                  the Revolving Credit Commitment exceeds an amount equal to PNC
                  Bank's Commitment less its Swing Loan Commitment, or if any
                  request by the Borrower for Loans would cause the aggregate
                  outstanding principal amount of the Loans made by PNC Bank
                  under the Revolving Credit Commitment to exceed an amount
                  equal to PNC Bank's Commitment less its Swing Loan Commitment,
                  then (A) the outstanding Swing Loans shall be reduced by a
                  Dollar amount necessary so that Loans under the Revolving
                  Credit Commitment can be made by PNC Bank in an aggregate
                  outstanding principal amount in excess of an amount equal to
                  PNC Bank's Commitment less its Swing Loan Commitment, and (B)
                  the Dollar amount of Swing Loans so reduced shall be
                  automatically converted by PNC Bank to Loans made by it under
                  the Revolving Credit Commitment.

                                    (iii) So long as PNC Bank elects to make
                  Swing Loans, PNC Bank shall, after receipt by it of a request
                  for a Swing Loan pursuant to Section 2.4b, fund such Swing
                  Loan to the Borrower by funding the account of the Borrower
                  maintained at PNC Bank or by PNC Bank making a wire transfer
                  into an account of the Borrower designated by the Borrower in
                  such request.


                  SECTION 1.03 AMENDMENTS TO SECTION 2.2 OF ORIGINAL CREDIT
                  AGREEMENT.

                  (a) Subsection 2.2a of the Original Credit Agreement is hereby
amended and restated in its entirety to read as follows:

                  2.2a INTEREST RATES. During the term hereof the Borrower, in
                  accordance with the provisions of this Section 2.2, shall have
                  the option of electing from time to time one or more of the
                  Interest Rate Options set forth below to be applied by the
                  Lenders to the Loans outstanding hereunder; PROVIDED, HOWEVER,
                  that only the Swing Loan Rate shall apply to the Swing Loans,
                  and PROVIDED, FURTHER, that if PNC Bank demands repayment of
                  the Swing Loans pursuant to Subsection 2.1g and the Lenders
                  are required to make Loans in the amount of their Ratable
                  Share of the Swing Loans, such Loans shall bear interest at
                  the Base Rate Option, until converted to another Interest Rate
                  Option:


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<PAGE>   8

                                    (i) BASE RATE AND EURO-RATE OPTIONS.
                  Interest (A) under the Base Rate Option shall accrue at a rate
                  per annum equal to the sum of (1) the Base Rate plus (2) the
                  Applicable Margin, as set forth below, and (B) under the
                  Euro-Rate Option shall accrue at a rate per annum equal to the
                  sum of (1) the Euro-Rate plus (2) the Applicable Margin, as
                  set forth below. In all cases the Applicable Margin shall
                  fluctuate in accordance with the Total Indebtedness to
                  Adjusted Annualized Operating Cash Flow Ratio, as follows:

<TABLE>
<CAPTION>

-----------------------------------------------------------------------------------------------------------
 TOTAL INDEBTEDNESS TO ADJUSTED ANNUALIZED                         APPLICABLE MARGIN
  OPERATING CASH FLOW RATIO AS OF THE LAST
  DAY OF THE IMMEDIATELY PRECEDING FISCAL
                  QUARTER
-----------------------------------------------------------------------------------------------------------
                                                                    BASE RATE                    EURO-RATE
-----------------------------------------------------------------------------------------------------------
<S>                                                                  <C>                            <C>   
Greater than 10.00:1.00                                              1.500%                         2.500%
-----------------------------------------------------------------------------------------------------------
Less than or equal to 10.00:1.00 but                                 1.250%                         2.250%
greater than 8.00:1.00
-----------------------------------------------------------------------------------------------------------
Less than or equal to 8.00:1.00 but greater                          1.000%                         2.000%
than 7.00:1.00
-----------------------------------------------------------------------------------------------------------
Less than or equal to 7.00:1.00 but greater                           .750%                         1.750%
than 6.00:1.00
-----------------------------------------------------------------------------------------------------------
Less than or equal to 6.00:1.00 but greater                           .500%                         1.500%
than 5.00:1.00
-----------------------------------------------------------------------------------------------------------
Less than or equal to 5.00:1.00 but greater                           .250%                         1.250%
than 4.00:1.00
-----------------------------------------------------------------------------------------------------------
Less than or equal to 4.00:1.00                                      0.000%                         1.000%
-----------------------------------------------------------------------------------------------------------
</TABLE>


                  (b) Subsection 2.2b(i) of the Original Credit Agreement is
hereby amended and restated in its entirety to read as follows:

                           (i) CHANGES IN TOTAL INDEBTEDNESS TO ADJUSTED
                  ANNUALIZED OPERATING CASH FLOW RATIO. Interest rate
                  adjustments resulting from changes in the Total Indebtedness
                  to Adjusted Annualized Operating Cash Flow Ratio shall be made
                  without notice to the Borrower, based on such ratio as of the
                  end of the most recently completed Fiscal Quarter. All
                  adjustments shall be determined when the Borrower's quarterly
                  financial statements 


                                      -8-
<PAGE>   9

                  and Compliance Certificate indicating such adjustment to be
                  warranted have been delivered to the Administrative Agent
                  pursuant to Section 5.2, and such adjustments will be
                  effective on the third Business Day following the date on
                  which such statements and Compliance Certificate were
                  delivered.

                  (c) Subsection 2.2h of the Original Credit Agreement is hereby
amended and restated in its entirety to read as follows:

                  2.2h INTEREST PAYMENT DATES. Interest due on all outstanding
                  Base Rate Loans and Swing Loans shall be payable quarterly in
                  arrears on the last day of each calendar quarter for the
                  calendar quarter just ended. The first payment of interest
                  under the Base Rate Option shall be due on December 31, 1996
                  and shall be for the actual number of days elapsed between the
                  Closing Date and such date. Interest due on all outstanding
                  Euro-Rate Loans shall be payable on the last day of each
                  Euro-Rate Interest Period and, for Euro-Rate Interest Periods
                  of six months or more, also quarterly in arrears on the last
                  day of each successive three-month period following the first
                  day of such Euro-Rate Interest Period. All accrued and unpaid
                  interest on the Loans and the Swing Loans shall be due and
                  payable on the Maturity Date and, after any maturity of the
                  Revolving Credit Notes, the Swing Note or the Obligations,
                  whether by acceleration or otherwise, on demand until all
                  amounts due hereunder are paid in full.

                  (d) Subsection 2.2i of the Original Credit Agreement is hereby
amended and restated in its entirety to read as follows:

                  2.2i CALCULATION OF INTEREST. Interest under the Base Rate
                  Option and under the Swing Loan Rate shall be calculated on
                  the basis of the actual number of days elapsed, using a year
                  of 365 or 366 days, as the case may be. Interest under the
                  Euro-Rate Option shall be calculated on the basis of the
                  actual number of days elapsed, using a year of 360 days.
                  Interest for any period shall be calculated from and including
                  the first day thereof to but not including the last day
                  thereof.


                  SECTION 1.04 AMENDMENT TO SECTION 2.4 OF ORIGINAL CREDIT
AGREEMENT. Section 2.4 of the Original Credit Agreement is hereby amended and
restated in its entirety to read as follows:

                  2.4 REQUESTS FOR LOANS, INTEREST RATE OPTIONS AND CONVERSIONS.

                                      -9-
<PAGE>   10

                                    (a) REVOLVING CREDIT LOANS. Each request for
                  a Loan and for the election, renewal or conversion to or of an
                  Interest Rate Option shall be made to the Administrative Agent
                  orally or in writing by an Authorized Officer no later than
                  12:00 noon (Eastern time) (i) at least one (1) Business Day
                  prior thereto, with respect to Base Rate Loans and (ii) at
                  least three (3) Business Days prior thereto, with respect to
                  Euro-Rate Loans. Any oral request for a Loan shall be followed
                  immediately by the Borrower's written confirmation of such
                  request, executed by an Authorized Officer, which confirmation
                  must set forth the amount and date of the Loan, the Interest
                  Rate Option selected and, if applicable, the Euro-Rate
                  Interest Period being selected. All written requests and
                  confirmations shall be in the form of Exhibit "B". A request
                  from the Borrower pursuant to this Section 2.4 with respect to
                  a Euro-Rate Loan shall irrevocably commit the Borrower to
                  accept such Euro-Rate Loan on the date specified in such
                  request. The Administrative Agent shall notify the Lenders of
                  each request for a Base Rate Loan or a Euro-Rate Loan as soon
                  as practicable, but not later than 12:00 noon (Eastern time)
                  on the date on which such Loan is to be made. Each Lender
                  shall make its Commitment Percentage of such Loan available to
                  the Borrower in immediately available funds at the principal
                  office of the Administrative Agent prior to 1:00 p.m. (Eastern
                  time) on the date such Loan is to be made.

                                    (b) SWING LOANS. Except as otherwise
                  provided herein, the Borrower may from time to time prior to
                  the Maturity Date request PNC Bank to make Swing Loans by
                  delivering to PNC Bank not later than 12:00 o'clock noon
                  Eastern time on the proposed borrowing date a duly completed
                  request therefor or a request by telephone immediately
                  confirmed in writing by letter, facsimile or telex. Each Swing
                  Loan Request shall be irrevocable and shall specify the
                  proposed borrowing date and the principal amount of such Swing
                  Loan, which shall be in the amounts specified in Section 2.1d
                  hereof.


                  SECTION 1.05 AMENDMENT TO SECTION 2.5 OF ORIGINAL CREDIT
AGREEMENT. Section 2.5 of the Original Credit Agreement is hereby amended and
restated in its entirety to read as follows:

                  2.5 METHOD OF DISBURSEMENTS AND PAYMENTS. All Loans (except
                  for Swing Loans, which shall be disbursed according to
                  Subsection 2.1g(i)) shall be made by the 


                                      -10-
<PAGE>   11

                  Administrative Agent funding the account of the Borrower
                  maintained at the Administrative Agent, if any, or by the
                  Administrative Agent making a wire transfer into an account of
                  the Borrower designated by the Borrower or as otherwise
                  directed by the Borrower to the Administrative Agent in
                  writing. All payments of principal, interest, Fees, costs and
                  other amounts due hereunder and under the other Loan Documents
                  relating to the Loans and the Revolving Credit Commitment
                  shall be made by the Borrower to the Administrative Agent at
                  the Administrative Agent's principal office at 909 Fannin,
                  Suite 1700, Houston, Texas 77010 not later than 2:00 p.m.
                  (Eastern time) on the due date. All payments of principal,
                  interest, Fees, costs and other amounts due hereunder and
                  under the other Loan Documents relating to the Swing Loans
                  shall be made by the Borrower to PNC Bank at PNC Bank's office
                  at 1600 Market Street, 21st Floor, Philadelphia, Pennsylvania
                  19103 no later than 2:00 p.m. (Eastern time) on the due date.
                  All such Loans and Swing Loans and payments thereof shall be
                  immediately good funds when either transferred by the
                  Administrative Agent or PNC Bank, as the case may be, to the
                  Borrower, or when delivered by the Borrower to the
                  Administrative Agent or PNC Bank, as the case may be.


                  SECTION 1.06 AMENDMENT TO SECTION 2.5 OF ORIGINAL CREDIT
AGREEMENT. Section 1.05 of the Original Credit Agreement is hereby amended and
restated in its entirety to read as follows:

                  2.6 LOAN ACCOUNTS. Each Lender shall open and maintain on its
                  books a Loan Account in the Borrower's name with respect to
                  Loans and Swing Loans made, repayments, prepayments, the
                  computation and payment of interest and other amounts due and
                  sums paid to such Lender hereunder and under the other Loan
                  Documents. Except in the case of manifest error in
                  computation, such records shall be presumed correct as to the
                  amount at any time due to such Lender from the Borrower. The
                  failure of any Lender to make an entry in its Loan Account
                  shall not abrogate the Borrower's duty to repay the
                  Obligations owned to such Lender.


                  SECTION 1.07 AMENDMENT TO SUBSECTION 2.7A OF ORIGINAL CREDIT
AGREEMENT. Subsection 2.7a of the Original Credit Agreement is hereby amended
and restated in its entirety to read as follows:

                  2.7a COMMITMENT FEE. (i) The Borrower shall pay to the
                  Administrative Agent, for the Pro Rata benefit of the Lenders,



                                      -11-
<PAGE>   12

                  on the last day of each calendar quarter during the term of
                  the Revolving Credit Commitment for the calendar quarter just
                  ended and on the Maturity Date, a Commitment Fee calculated on
                  the basis of the actual number of days elapsed, using a year
                  of 365 or 366 days, as the case may be, at the following
                  rates:

<TABLE>

<S>                                                                <C>   
                  At all times when the ratio of                   0.375%
                  Total Indebtedness to Adjusted 
                  Annualized Operating Cash Flow
                  is greater than or equal to 6.00 to 1.00

                  At all times when the ratio of                   0.250%
                  Total Indebtedness to Adjusted
                  Annualized Operating Cash Flow
                  is less than 6.00 to 1.00
</TABLE>

                  computed on the average daily (computed at the opening of
                  business) unused amount of the Revolving Credit Commitment;
                  PROVIDED, HOWEVER, that the Borrower shall not pay the
                  Commitment Fee with respect to PNC Bank's Swing Loan
                  Commitment. The first payment of the Commitment Fee shall be
                  due on December 31, 1996 and shall be for the actual number of
                  days elapsed between the Closing Date and such date.

                           (ii) Commitment fee adjustments resulting from
                  changes in the Total Indebtedness to Adjusted Annualized
                  Operating Cash Flow Ratio shall be made without notice to the
                  Borrower, based on such ratio as of the end of the most
                  recently completed Fiscal Quarter. All adjustments shall be
                  determined when the Borrower's quarterly financial statements
                  and Compliance Certificate indicating such adjustment to be
                  warranted have been delivered to the Administrative Agent
                  pursuant to Section 5.2, and such adjustments will be
                  effective on the third Business Day following the date on
                  which such statements and Compliance Certificate were
                  delivered.


                  SECTION 1.08 AMENDMENT TO SUBSECTION 8.1A. Subsection 8.1a of
the Original Credit Agreement is hereby amended and restated to read as follows:

                  8.1a NONPAYMENT OF BORROWER'S OBLIGATIONS. The Borrower shall
                  default (i) in any payment or required prepayment of principal
                  of the Loans or the Swing Loans when due or any scheduled
                  Revolving Credit Commitment reduction when due, or (ii) in the
                  payment of interest on any Loans or Swing Loans when 


                                      -12-
<PAGE>   13

                  due, or in the payment of any of the Fees, expenses or other
                  amounts due hereunder or under any of the other Loan Documents
                  when due, and such default in payment of interest, Fees,
                  expenses or other amounts shall have continued for a period of
                  five (5) Business Days after such due date.


                  SECTION 1.09 AMENDMENTS TO SECTION 8.2. Subsections 8.2a and
8.2b of the Original Credit Agreement are hereby amended and restated to read as
follows:

                  8.2a EVENTS OF DEFAULT UNDER SECTIONS 8.1C AND 8.1D. Upon the
                  occurrence of an Event of Default set forth in Sections 8.1c
                  and 8.1d, the Revolving Credit Commitment shall automatically
                  terminate and automatically the Revolving Credit Notes, the
                  Swing Loan Note, interest accrued thereon, all other
                  Obligations of the Borrower and all obligations, if any, of
                  any Subsidiary of the Borrower or Wireless under any Loan
                  Document to the Lenders and the Agents shall all become
                  immediately due and payable, without the necessity of demand,
                  presentation, protest, notice of dishonor or notice of
                  default, all of which are hereby expressly waived and deemed
                  to be waived by the Borrower, any Subsidiary of the Borrower
                  or Wireless. Thereafter, the Lenders shall have no further
                  obligation to make any additional Loans hereunder and PNC Bank
                  shall have no further obligation to make any additional Swing
                  Loans hereunder. In addition, during any 60-day period
                  described in Section 8.1c(i), the Lenders shall not have any
                  obligation to make any additional Loans (except in accordance
                  with Subsection 2.1g(i) hereof) and PNC Bank shall not have
                  any obligation to make any additional Swing Loans hereunder.

                  8.2b REMAINING EVENTS OF DEFAULT. Upon the occurrence and
                  during the continuance of any Event of Default set forth in
                  Sections 8.1a, 8.1b, 8.1e, 8.1f, 8.1g, 8.1h, 8.1i, 8.1j, 8.1k,
                  8.1l or 8.1m, the Required Lenders may, at their option,
                  declare the Revolving Credit Commitment terminated and the
                  Revolving Credit Notes, the Swing Note, interest accrued
                  thereon, all other Obligations of the Borrower and all
                  obligations, if any, of any Subsidiary of the Borrower or
                  Wireless under any Loan Document to the Lenders and the Agents
                  to be due and payable, without the necessity of demand,
                  presentation, protest, notice of dishonor or notice of
                  default, all of which are hereby expressly waived and deemed
                  to be waived by the Borrower, any Subsidiary of the Borrower
                  or Wireless. Thereafter, the Lenders shall have no further
                  obligation to make any additional Loans hereunder (except 


                                      -13-
<PAGE>   14

                  in accordance with Subsection 2.1g(i) hereof), and PNC Bank
                  shall have no further obligation to make any additional Swing
                  Loans hereunder.


                  SECTION 1.10 AMENDMENT TO SECTION 10.1. Section 10.1 of the
Original Credit Agreement is hereby amended by adding the following paragraph
(iv) immediately following paragraph (iii):

                                    (iv) The foregoing provisions of this
                  Section 10.1 notwithstanding, PNC Bank and the Borrower may,
                  without the consent or approval of any Lender or any Agent,
                  take the following actions with respect to the Swing Loans and
                  the Swing Loan Commitment:

                                            (A) Adjust the Swing Loan Rate; and

                                            (B) Make changes to the methods of
                  payments of and disbursements of Swing Loans.


                  SECTION 1.11 AMENDMENTS TO EXHIBITS. The Original Credit
Agreement is hereby amended to include EXHIBIT "A" which is attached to this
Second Amendment.


                  SECTION 1.12 NO OTHER AMENDMENTS OR WAIVERS. The amendments to
the Original Credit Agreement set forth above do not either implicitly or
explicitly alter, waive or amend, except as expressly provided in this Second
Amendment, the provisions of the Original Credit Agreement. The amendments set
forth above do not waive, now or in the future, compliance with any other
covenant, term or condition to be performed or complied with nor do they impair
any rights or remedies of the Lenders or the Agents under the Original Credit
Agreement or any other Loan Document with respect to any such violation. Nothing
in this Second Amendment shall be deemed or construed to be a waiver or release
of, or a limitation upon, the Agents' or the Lenders' exercise of any of their
respective rights and remedies under the Original Credit Agreement and the other
Loan Documents, whether arising as a consequence of any Events of Default which
may now exist or otherwise, and all such rights and remedies are hereby
expressly reserved.


                                   ARTICLE II

                     BORROWER'S SUPPLEMENTAL REPRESENTATIONS
                     ---------------------------------------

                  SECTION 2.01. INCORPORATION BY REFERENCE. As an inducement to
the Lenders and the Agents to enter into this Second Amendment, the Borrower
hereby repeats herein for the 


                                      -14-
<PAGE>   15

benefit of the Lenders and the Agents the representations and warranties made by
the Borrower in Article 4 of the Original Credit Agreement, as amended hereby,
except that for purposes hereof such representations and warranties shall be
deemed to extend to and cover this Second Amendment and the Swing Loan Note.


                                   ARTICLE III

                              CONDITIONS PRECEDENT
                              --------------------

                  SECTION 3.01 CONDITIONS PRECEDENT. Each of the following shall
be a condition precedent to the effectiveness of this Second Amendment:

                  (i) The Documentation Agent shall have received, on or before
the Amendment Effective Date (as hereinafter defined), the following items,
each, unless otherwise indicated, dated on or before the Amendment Effective
Date and in form and substance satisfactory to the Documentation Agent and its
special counsel, Tucker Arensberg, P.C.:

                           (A) Counterpart originals of this Second Amendment
duly executed by the Borrower, each Lender and each Agent;

                           (B) The Swing Loan Note, duly executed by the
Borrower; and

                           (C) A certified copy of the corporate action of the
Borrower authorizing the execution and delivery of and the performance under
this Second Amendment and the Swing Loan Note.

                  For purposes of this Second Amendment the term "Amendment
Effective Date" means the date on which the Documentation Agent and its counsel
have determined that each of the conditions set forth in this Section 3.01 has
been satisfied by the Borrower or waived by the Lenders.




                                      -15-
<PAGE>   16



                                   ARTICLE IV

                               GENERAL PROVISIONS
                               ------------------

                  SECTION 4.01 RATIFICATION OF TERMS. Except as expressly
amended by this Second Amendment, the Original Credit Agreement and each and
every representation, warranty, covenant, term and condition contained therein
is specifically ratified and confirmed by the Borrower.

                  SECTION 4.02 REFERENCES. All notices, communications,
agreements, certificates, documents or other instruments executed and delivered
after the execution and delivery of this Second Amendment in connection with the
Original Credit Agreement, any of the other Loan Documents or the transactions
contemplated thereby may refer to the Original Credit Agreement without making
specific reference to this Second Amendment, but nevertheless all such
references shall include this Second Amendment unless the context requires
otherwise. From and after the Amendment Effective Date, all references in the
Original Credit Agreement and each of the other Loan Documents to the
"Agreement" shall be deemed to be references to the Original Credit Agreement as
amended hereby.


                  SECTION 4.03 INCORPORATION INTO AGREEMENT. This Second
Amendment is deemed incorporated into the Agreement. To the extent that any term
or provision of this Second Amendment is or may be deemed expressly inconsistent
with any term or provision of the Agreement, the terms and provisions hereof
shall control.


                  SECTION 4.04 COUNTERPARTS. This Second Amendment may be
executed in any number of separate counterparts, each of which, when so executed
and delivered, shall be regarded as an original, and all such counterparts shall
together constitute one and the same instrument.


                  SECTION 4.05 CAPITALIZED TERMS. Except for proper nouns and as
otherwise defined herein, capitalized terms used herein as defined terms shall
have the meanings ascribed to them in the Original Credit Agreement, as amended
hereby.


                  SECTION 4.06 COSTS AND EXPENSES. The Borrower will pay all
costs and expenses of the Documentation Agent (including, without limitation,
the reasonable fees and the disbursements of the Documentation Agent's special
counsel, Tucker Arensberg, P.C.) in connection with the preparation, execution
and delivery of this Second Amendment and the other documents, instruments and
certificates delivered in connection herewith.


                                      -16-
<PAGE>   17


                  SECTION 4.07 GOVERNING LAW. THIS SECOND AMENDMENT SHALL BE
GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE COMMONWEALTH OF
PENNSYLVANIA, WITHOUT REGARD TO THE PRINCIPLES THEREOF REGARDING CONFLICTS OF
LAW, EXCEPTING APPLICABLE FEDERAL LAW AND EXCEPT ONLY TO THE EXTENT PRECLUDED BY
THE MANDATORY APPLICATION OF THE LAW OF ANOTHER JURISDICTION.

                  SECTION 4.08 HEADINGS. The headings of the sections in this
Second Amendment are for purposes of reference only and shall not be deemed to
be a part hereof.


                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]



                                      -17
<PAGE>   18


                  IN WITNESS WHEREOF, the parties hereto, with the intent to be
legally bound hereby, have caused this Second Amendment to Credit Agreement to
be duly executed by their respective proper and duly authorized officers as a
document under seal, as of the day and year first above written.

ATTEST/WITNESS:                    SYGNET COMMUNICATIONS, INC.


                                   By:                               (SEAL)
---------------------------------     -------------------------------
Name:                              Name:
Title:                             Title:


                                   TORONTO DOMINION (TEXAS), INC.,
                                   in its capacity as Administrative Agent


                                   By:                           (SEAL)
                                      ---------------------------
                                   Name:
                                   Title:


                                   PNC BANK, NATIONAL ASSOCIATION,
                                   in its capacities as Documentation Agent and
                                   Collateral Agent and as a Lender


                                   By:                                (SEAL)
                                      --------------------------------
                                   Name:
                                   Title:


                                   THE TORONTO-DOMINION BANK


                                   By:                                (SEAL)
                                      --------------------------------
                                   Name:
                                   Title:


                                      -18
<PAGE>   19

                                   CIBC, INC.


                                   By:                                (SEAL)
                                      --------------------------------
                                   Name:
                                   Title:


                                   CORESTATES BANK, N.A.


                                   By:                                (SEAL)
                                      --------------------------------
                                   Name:
                                   Title:


                                   FLEET NATIONAL BANK


                                   By:                               (SEAL)
                                       ------------------------------
                                   Name:
                                   Title:


                                   CREDIT LYONNAIS


                                   By:                              (SEAL)
                                       -----------------------------
                                   Name:
                                   Title:


                                   THE FIRST NATIONAL BANK OF
                                   MARYLAND


                                   By:                              (SEAL)
                                       -----------------------------
                                   Name:
                                   Title:


                                      -19-
<PAGE>   20

                                   UNION BANK OF CALIFORNIA, N.A.


                                   By:                              (SEAL)
                                       -----------------------------
                                   Name:
                                   Title:


                                   BANK OF MONTREAL, CHICAGO BRANCH


                                   By:                              (SEAL)
                                       -----------------------------
                                   Name:
                                   Title:


                                   ROYAL BANK OF CANADA


                                   By:                              (SEAL)
                                       -----------------------------
                                   Name:
                                   Title:


                                   NATIONAL CITY BANK,
                                   successor-in-interest to
                                   National City Bank Northeast

                                   By:                              (SEAL)
                                       -----------------------------
                                   Name:
                                   Title:





                                      -20
<PAGE>   21


                                   MERITA BANK LTD - NEW YORK BRANCH


                                   By:                              (SEAL)
                                       -----------------------------
                                   Name:
                                   Title:


                                   By:                              (SEAL)
                                       -----------------------------
                                   Name:
                                   Title:


                                   THE MAHONING NATIONAL BANK OF
                                   YOUNGSTOWN


                                   By:                             (SEAL)
                                       -----------------------------
                                   Name:
                                   Title:






                                      -21-