Document:

<PAGE>

                                                                    Exhibit 10.8

                              SIXTH AMENDMENT TO
                      AMENDED AND RESTATED LOAN AGREEMENT

     THIS SIXTH  AMENDMENT TO AMENDED AND RESTATED LOAN  AGREEMENT,  dated as of
the 26th day of October, 2001 (this "Amendment"),  is made by and among AMERICAN
                                     ---------
TOWER, L.P., a Delaware limited  partnership,  AMERICAN TOWERS, INC., a Delaware
corporation, VERESTAR, INC. (f/k/a ATC TELEPORTS, INC.), a Delaware corporation,
and TOWERSITES  MONITORING,  INC., a Delaware  corporation,  (collectively,  the
"Borrowers"), THE FINANCIAL INSTITUTIONS SIGNATORIES HERETO and TORONTO DOMINION
 ---------
(TEXAS),  INC., as administrative  agent (in such capacity,  the "Administrative
                                                                  --------------
Agent").
-----

                             W I T N E S S E T H:
                             - - - - - - - - - -

     WHEREAS, the Borrowers, the Lenders (as defined therein), the Issuing Bank
(as defined therein) and the Administrative Agent are all parties to that
certain Amended and Restated Loan Agreement dated as of January 6, 2000 (as
previously amended and as hereafter amended, modified, restated and supplemented
from time to time, the "Loan Agreement"); and
                        --------------

     WHEREAS, the Borrowers have requested amendments to certain provisions of
the Loan Agreement, and, subject to the terms and conditions set forth herein,
the Lenders and the Administrative Agent are willing to amend certain provisions
of the Loan Agreement as more specifically set forth herein;

     NOW, THEREFORE, in consideration of the premises set forth above, and other
good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto hereby agree that all capitalized terms used
and not defined herein shall have the meanings ascribed to such terms in the
Loan Agreement, and further hereby agree as follows:

     1.       Amendments.  The Loan Agreement is hereby amended as more
              ----------
fully set for the below:

              (a)      Amendments to Article 1.
                       -----------------------

                              (i) Section 1.1 of the Loan Agreement,
          Definitions, is hereby amended by deleting the definitions of
          -----------
          "Annualized Operating Cash Flow", "ATC International" "Borrowers",
           ------------------------------    -----------------   ---------
          "Change of Control" "Pro Forma Debt Service" and "Restricted
           -----------------   ----------------------       ----------
          Subsidiaries" in their entirety and by substituting the following
          ------------
          definitions in lieu thereof:

                       " 'Annualized Operating Cash Flow' shall mean, as of
                          ------------------------------
                  any calculation date, in each case on a consolidated basis,
                  (a) the sum of (i) the product of (A) Operating Cash Flow
                  (Mature Towers) for the fiscal quarter-end being tested, or
<PAGE>

                  the most recently completed fiscal quarter immediately
                  preceding such calculation date, as the case may be, times (B)
                                                                       -----
                  four (4); and (ii) the product of (A) Operating Cash Flow
                  (Developing Towers) for the fiscal quarter-end being tested,
                  or the most recently completed fiscal quarter immediately
                  preceding such calculation date, as the case may be, times (B)
                                                                       -----
                  four (4); and (iii) Operating Cash Flow (Other Business) for
                  the four fiscal quarter period end being tested or the most
                  recently completed four (4) fiscal quarter period immediately
                  preceding such calculation date, as the case may be; minus (b)
                                                                       -----
                  corporate overhead (exclusive of amortization and
                  depreciation) of the Borrowers and the Restricted Subsidiaries
                  for the four (4) fiscal quarter period then ended or, the most
                  recently completed four (4) fiscal quarter period immediately
                  preceding the calculation date, as the case may be; provided,
                                                                      --------
                  however, that for purposes of calculating the Leverage Ratio
                  -------
                  only, (I) item (a) above shall not include the amount by which
                  the product of (x) Operating Cash Flow (without deductions for
                  corporate overhead) attributable to Restricted Subsidiaries
                  located in or doing business in Brazil and Mexico (or such
                  other countries as the Majority Lenders approve) times (y)
                  four (4) exceeds ten percent (10%) of the total amount
                  determined by clause (a) of this definition (before giving
                  effect to the deduction set forth in clause (II) immediately
                  following), and (II) item (a)(iii) above shall be reduced by
                  twenty-five percent (25%)."

                       " 'ATC International' shall mean American Tower
                          -----------------
                  International, Inc., a Delaware corporation."

                       "'Borrowers' shall mean, collectively, AT L.P., AT Inc.,
                         ---------
                  Verestar, Inc. (f/k/a ATC Teleports), Towersites Monitoring,
                  Inc., a Delaware corporation, and ATC International, and shall
                  include such other Persons as may be approved by the Majority
                  Lenders at such time as any such Person executes and delivers
                  to the Administrative Agent an assignment and assumption
                  agreement in form and substance satisfactory to the
                  Administrative Agent and each other Loan Document as executed
                  by the other Borrowers; and "Borrower" shall mean any one of
                                               --------
                  the foregoing."

                       " 'Change of Control' shall mean (a) the failure of the
                          -----------------
                  Parent to own, directly or indirectly, one hundred percent
                  (100%) of the ownership interests of each of the Borrowers,
                  except for Verestar, of which the Parent must own ninety
                  percent (90%), provided that the remaining ten percent (10%)
                                 --------
                  of Verestar is held by other Persons in connection with an
                  employee stock option plan, (b) the failure of AT Inc. to own,
                  directly or indirectly, one hundred percent (100%) of the
                  ownership interests of ATC Operating (unless ATC Operating is
                  merged with or into AT Inc.), (c) the sale, lease, transfer,
                  in one or a series of related transactions, of all or
                  substantially all of any of the Borrower's assets to any
                  Person or group (as such term is used in Section 13(d)(3) of
                  the Exchange Act) other than to the other Borrowers or any
                  wholly-owned direct or indirect Restricted Subsidiary of AT
                  Inc., (d) the adoption of a plan relating to the liquidation
                  or dissolution of the

                                      -2-
<PAGE>

                  Parent, (e) the acquisition, directly or indirectly, by any
                  Person or group (as such term is used in Section 13(d)(3) of
                  the Exchange Act) of forty percent (40%) or more of the voting
                  power of the voting stock of the Parent by way of merger or
                  consolidation or otherwise and such Persons own more voting
                  power than the Principal Shareholders, or (f) the Continuing
                  Directors cease for any reason to constitute a majority of the
                  directors of the Parent then in office."

                       " 'Pro Forma Debt Service' shall mean with respect to the
                          ----------------------
                  twelve (12) calendar month period following the calculation
                  date, and after giving effect to any Interest Hedge Agreements
                  and LIBOR Advances, the sum of the amount of all of the
                  following with respect to the Borrowers and the Restricted
                  Subsidiaries, on a consolidated basis: (a) scheduled payments
                  of principal on Indebtedness for Money Borrowed (determined,
                  with respect to the Revolving Loans only, as the difference
                  between the outstanding principal amount of the Revolving
                  Loans and Letter of Credit Obligations on the calculation date
                  and the amount the Revolving Loan Commitments will be on the
                  last day of such period) for such period; (b) Interest Expense
                  for such period; (c) fees payable under this Agreement for
                  such period; (d) other payments payable by such Persons during
                  such period in respect of Indebtedness for Money Borrowed
                  (other than voluntary repayments); and (e) after the Interest
                  Reserve, the 2001 Interest Reserve and/or the 2002 Interest
                  Reserve, as applicable, has been applied in full pursuant to
                  the terms hereof, all Restricted Payments to be made by the
                  Borrowers to the Parent which will be necessary to make
                  interest payments on the (i) Convertible Notes and/or (ii)
                  Senior Notes due 2009 during such period. For purposes of this
                  definition, where interest payments for the twelve (12) month
                  period immediately succeeding the calculation date are not
                  fixed by way of Interest Hedge Agreements, LIBOR Advances, or
                  otherwise for the entire period, interest shall be calculated
                  on such Indebtedness for Money Borrowed for periods for which
                  interest payments are not so fixed at the lesser of (i) the
                  LIBOR Basis (based on the then current adjustment under
                  Section 2.3(f) hereof) for a LIBOR Advance having an Interest
                  Period of six (6) months as determined on the date of
                  calculation and (ii) the Base Rate Basis as in effect on the
                  date of calculation; provided, however, that if such LIBOR
                                       --------  -------
                  Basis cannot be determined in the reasonable opinion of the
                  Administrative Agent, such interest shall be calculated using
                  the Base Rate Basis as then in effect."

                       " 'Restricted Subsidiary' shall mean any Subsidiary of
                          ---------------------
                  any Borrower other than an Unrestricted Subsidiary which (a)
                  is organized under the laws of, or owns, operates, constructs,
                  or manages towers in the United States of America, Brazil or
                  Mexico, provided that such Subsidiary (i) is permitted to pay
                          --------
                  dividends, (ii) has no liens other than Permitted Liens and
                  (iii) that such Subsidiary becoming a Restricted Subsidiary
                  shall not cause a Default or Event of Default, or in such
                  other jurisdictions as the Majority Lenders may from time to
                  time approve by prior written consent; and (b) has complied
                  with the requirements of Section 5.13

                                      -3-
<PAGE>

                  hereof (or delivered comparable documents to effect the
                  purpose of such Section 5.13). The Restricted Subsidiaries as
                  of the Agreement Date are as set forth on Schedule 2 attached
                                                            ----------
                  hereto.

                            (ii) Section 1.1 of the Loan Agreement, Definitions,
                                                                    -----------
          is hereby amended by inserting the new definitions of "2002 Interest
                                                                 -------------
          Reserve" and "Term Loan C Loans" in the proper alphabetical order:
          -------       -----------------

                       " '2002 Interest Reserve' shall mean an escrow account
                          ---------------------
                  pledged to the Lenders as collateral which is (a) maintained
                  by one of the Borrowers, (b) maintained with the
                  Administrative Agent on terms and conditions satisfactory to
                  the Administrative Agent, (c) established with cash proceeds
                  in an amount equal to $46,875,000.00 and (d) so long as no
                  Event of Default has occurred and is continuing, used to make
                  interest payments due in August 2002 on the Senior Notes due
                  2009."

                       " 'Term Loan C Loans' shall mean, collectively, the
                          -----------------
                  amounts advanced in connection with the Notice of Incremental
                  Facility Commitment for Term Loan C."

                  (b)  Amendments to Article 2.
                       -----------------------

                       (i) Section 2.7(b)(v) of the Loan Agreement, Sale of
          Capital Stock and Debt Instruments, is hereby amended by deleting such
          section in its entirety and substituting in lieu thereof the
          following:

                                "(v)    Sale of Capital Stock and Debt
                                        ------------------------------
                                        Instruments.
                                        -----------

                                 (A)    Capital Stock. At any time when there
                                        -------------
                  are Term Loan C Loans outstanding, on the Business Day
                  following the date of receipt by the Parent, any Borrower or
                  any Restricted Subsidiary of any net cash proceeds from the
                  sale of any Capital Stock by any of the Parent, any Borrower,
                  or any Restricted Subsidiary (other than (x) net proceeds in
                  an amount not to exceed $2,000,000.00 in the aggregate after
                  the Agreement Date from the sale or issuance of Capital Stock
                  in connection with any employee stock option plan of such
                  Person or (y) proceeds received from Capital Stock issued in
                  connection with an Acquisition permitted hereunder), the Term
                  Loan C Loans shall be repaid (or, if no Term Loan C Loans are
                  outstanding, the Term Loan C Loan commitment shall be
                  cancelled) by an amount equal to such net cash proceeds;
                  provided, however, that if such net cash proceeds are received
                  --------  -------
                  on or prior to April 30, 2002 and no Term Loan C Loans are
                  then outstanding, the Term Loan C Loan commitment shall be
                  cancelled by an amount equal to such net cash proceeds in
                  excess of $200,000,000.00, as more fully set forth in the
                  Notice of Incremental Facility Commitment dated as of October
                  26, 2001;

                                      -4-
<PAGE>

                                 (B)    Debt Instruments. On the Business Day
                                        ----------------
                  following the date of receipt by the Parent, any Borrower or
                  any Restricted Subsidiary of (1) at any time when there are
                  Term Loan C Loans and/or Term Loan C Loan commitments
                  outstanding, any net cash proceeds from the issuance of any
                  public or private debt by any of the Borrowers, any of the
                  Restricted Subsidiaries or the Parent, the Term Loan C Loans
                  shall be repaid in an amount equal to such net cash proceeds
                  (or if no Term Loan C Loans are then outstanding, the Term
                  Loan C Loan commitment shall be reduced, as more fully set
                  forth in the Notice of Incremental Facility dated as of
                  October 26, 2001), and (2) at any time when there are no Term
                  Loan C Loans outstanding, any Capital Raise Proceeds, the
                  Loans shall be repaid in an amount equal to, in the aggregate,
                  the Capital Raise Proceeds (after deducting amounts applied to
                  Term Loan C Loans).

                                 (C)    Application of Proceeds. The amount of
                                        -----------------------
                  the Capital Raise Proceeds required to be repaid under Section
                  2.7(b)(v)(B)(2) shall be applied to the Loans then outstanding
                  on a pro rata basis. Accrued interest on the principal amount
                  of the Loans being prepaid pursuant to Section 2.7(b)(v) to
                  the date of such prepayment will be paid by the Borrowers
                  concurrently with such principal prepayment. All repayments
                  under this Section 2.7(b)(v) of each of the Term Loan A Loans
                  and the Term Loan B Loans shall be applied to the repayments
                  for such Loans in Section 2.7(b)(i) hereof in inverse order of
                  maturity. All repayments under this Section 2.7(b)(v) of the
                  Term Loan C Loans shall be applied to the repayments for such
                  Term Loan C Loans in inverse order of maturity.
                  Notwithstanding anything to the contrary in this Agreement, to
                  the extent that net cash proceeds from a sale of Capital Stock
                  and an issuance of public or private debt are received on the
                  same day, the net cash proceeds from the issuance of public or
                  private debt shall be applied to the Term Loan C Loans first,
                  up to 50% of the total amount of such issuance, including
                  amounts applied to the Term Loan C Loans, shall be deemed
                  Capital Raise Proceeds (unless specifically excluded in the
                  definition thereof), and any remaining Capital Raise Proceeds
                  shall then be used to repay the Loans (other than the Term
                  Loan C Loans) in accordance with Section 2.7(b)(v)(B). Any
                  amendments or waivers of this Section 2.7(b)(v) shall require
                  the approval of at least 50.1% of lenders holding Term Loan C
                  Loans and/or Term Loan C Loan commitments as well as the
                  approval of the Majority Lenders."

                           (ii) Section 2.15 of the Loan Agreement, Incremental
          Facility Advances, is hereby amended by adding new section 2.15(f) as
          set forth below:

                           "(f)  Notwithstanding anything to the contrary
                  herein, (i) the Term Loan C Loans may be refinanced in whole
                  or in part with other Incremental Facility Loans (each, a
                  "Replacement Term Loan C Loan"), which Replacement Term Loan C
                   ----------------------------
                  Loan shall not reduce the amount of the then available
                  remaining

                                      -5-
<PAGE>

                  Incremental Facility Commitment, and (ii) to the extent the
                  Term Loan C Loans are repaid (or the commitment for such Term
                  Loan C Loans is cancelled in whole or in part) as a result of
                  the receipt by the Borrowers, the Restricted Subsidiaries or
                  the Parent of the net cash proceeds from (A) the sale of any
                  Capital Stock or (B) the issuance of any non-pari passu public
                  or private debt otherwise permitted under this Agreement, the
                  then available Incremental Facility Commitment will be
                  increased by an amount equal to such repayment (or commitment
                  cancellation)."

                  (b)      Amendments to Article 7.
                           -----------------------

                           (i) Section 7.6 of the Loan Agreement, Investments
                                                                  -----------
          and Acquisitions, is hereby amended by deleting subsection (b) thereof
          ----------------
          in its entirety and substituting in lieu thereof the following:

                           "(b)     so long as no Default then exists or would
                  be caused thereby, establish Unrestricted Subsidiaries and
                  make Investments in (i) such Unrestricted Subsidiaries (in
                  addition to Investments permitted under Section 7.6(e), (f)
                  and (g) hereof), (ii) [reserved] and (iii) Persons primarily
                  engaged in domestic and foreign communications tower and tower
                  related businesses in an aggregate amount, directly or
                  indirectly, provided that, giving effect to such additional
                              --------
                  Investment, the aggregate Net Investment Amount made pursuant
                  to the provisions of this Section 7.6(b) shall not exceed,
                  from and after the effective date of the Sixth Amendment to
                  Amended and Restated Loan Agreement, $300,000,000.00 at any
                  time; provided further that, in the case of Investments made
                        -------- -------
                  pursuant to clause (iii) of this Section 7.6(b), the Parent,
                  any Borrower or any of the Restricted Subsidiaries has
                  executed a binding acquisition, merger, lease/sublease or
                  management agreement with such Person;"

                           (ii) Section 7.6 of the Loan Agreement, Investments
                                                                   -----------
          and Acquisitions, is hereby amended by deleting subsection (f) thereof
          ----------------
          in its entirety and substituting in lieu thereof the following:

                           "(f)     [RESERVED]"

                           (iii) Section 7.7 of the Loan Agreement, Restricted
                                                                    ----------
          Payments, is hereby amended by deleting such section in its entirety
          --------
          and substituting in lieu thereof the following:

                           "Section 7.7 Restricted Payments. The Borrowers shall
                                        -------------------
                  not, and shall not permit any of the Restricted Subsidiaries
                  to, directly or indirectly declare or make any Restricted
                  Payment; provided, however, that so long as no Default or
                           --------  -------
                  Event of Default hereunder then exists or would be caused
                  thereby, the Borrowers may make, (a) subject to Section
                  2.7(b)(iv) hereof, cash distributions in an

                                      -6-
<PAGE>

                  aggregate amount for all Borrowers not to exceed fifty percent
                  (50%) of Excess Cash Flow for the immediately preceding
                  calendar year, on or after April 15th of each calendar year
                  commencing on April 15, 2004; and (b) distributions to the
                  Parent to make scheduled principal and interest payments on
                  the Convertible Notes and the Senior Notes due 2009; provided,
                                                                       --------
                  however, that (x) all funds in the Interest Reserve shall have
                  -------
                  been used to make all interest payments on the Convertible
                  Notes due on or prior to October 15, 2001, (y) all funds in
                  the 2001 Interest Reserve shall have been used in full to make
                  all interest payments on the Senior Notes due 2009 due on or
                  prior to February 15, 2002 and (z) all funds in the 2002
                  Interest Reserve shall have been used to make all interest
                  payments on the Senior Notes due 2009 due in August 2002;
                  provided that any funds remaining in the 2001 Interest Reserve
                  --------
                  shall be used in full for such payments prior to using funds
                  in the 2002 Interest Reserve."

                           (iv) Section 7.8 of the Loan Agreement, Leverage
                                                                   --------
          Ratio, is hereby amended by deleting the table included in such
          -----
          section in its entirety and substituting in lieu thereof the following
          new table:

                  "Period                                                 Ratio
                   ------                                                 -----

                  Borrowing Base Termination Date
                  through December 31, 2001                        7.75 to 1.00

                  January 1, 2002 through
                  March 31, 2002                                   7.50 to 1.00

                  April 1, 2002 through
                  June 30, 2002                                    7.00 to 1.00

                  July 1, 2002 through
                  September 30, 2002                               6.75 to 1.00

                  October 1, 2002 through
                  March 31, 2003                                   6.50 to 1.00

                  April 1, 2003 through
                  September 30, 2003                               6.00 to 1.00

                  October 1, 2003 through
                  March 31, 2004                                   5.25 to 1.00

                  April 1, 2004 through
                  September 30, 2004                               4.75 to 1.00

                                      -7-
<PAGE>

                  October 1, 2004 through
                  March 31, 2005                                   4.25 to 1.00

                  April 1, 2005 and thereafter                     4.00 to 1.00"

         2.  No Other Amendments. Except for the amendments set forth above, the
             -------------------
text of the Loan Agreement and all other Loan Documents shall remain unchanged
and in full force and effect. No amendment, waiver or consent by the
Administrative Agent, the Issuing Bank or the Lenders under the Loan Agreement
or any other Loan Document is granted or intended except as expressly set forth
herein, and the Administrative Agent, the Issuing Bank and the Lenders expressly
reserve the right to require strict compliance in all other respects (whether or
not in connection with any Requests for Advance). Except as set forth herein,
the amendments agreed to herein shall not constitute a modification of the Loan
Agreement or any of the other Loan Documents, or a course of dealing with the
Administrative Agent, the Issuing Bank and the Lenders at variance with the Loan
Agreement or any of the other Loan Documents, such as to require further notice
by the Administrative Agent, the Issuing Bank, the Lenders or the Majority
Lenders to require strict compliance with the terms of the Loan Agreement and
the other Loan Documents in the future.

         3.  Conditions Precedent.  The effectiveness of this Amendment is
             --------------------
subject to:

         (a) receipt by the Administrative Agent of the following:

             (i)      duly executed signature pages to this Amendment from the
             Majority Lenders;

             (ii)     a duly executed Security Agreement from American Tower
             International, Inc.;

             (iii)    a duly executed Pledge Agreement from American Tower
             International, Inc., pledging its interests in ATC Mexico Holding
             Corp., a Delaware corporation, and ATC South America Holding Corp.,
             a Delaware corporation;

             (iv)     a duly executed Assumption Agreement, in form and
             substance acceptable to the Administrative Agent, from American
             Tower International, Inc.;

             (v)      a loan certificate of American Tower International, Inc.,
             in substantially in the form of Exhibit V attached to the Loan
             Agreement, with all exhibits thereto;

             (vi)     UCC-1 financing statements signed by American Tower
             International, Inc. to be filed in the office of the Secretary of
             State of the State of Delaware; and

             (vii)   evidence that the 2002 Interest Reserve has been
             established;

                                      -8-
<PAGE>

         (b)     payment from funds received from the Borrowers by the
Administrative Agent to each Lender approving this Amendment of an amendment fee
equal to three-sixteenths (3/16) of one percent of the amount of Term Loan A
Loans, Term Loan B Loans and Revolving Loan Commitments held by such Lender; and

         (c)     the representations and warranties contained in Article 4 of
the Loan Agreement and contained in the other Loan Documents remaining true and
correct as of the date hereof, both before and after giving effect to this
 Agreement, except to the extent previously fulfilled in accordance with the
terms of the Loan Agreement or such other Loan Document, as applicable, or to
 the extent relating specifically to the earlier date.  No Default or Event of
Default now exists or will be caused hereby.

          4.     Counterparts.  This Amendment may be executed in any number of
                 ------------
counterparts,  each of which  shall be  deemed to be an  original,  but all such
separate counterparts shall together constitute but one and the same instrument.

          5.     Governing Law. This Amendment shall be construed in accordance
                 -------------
with and governed by the laws of the State of New York.

          6.     Severability.  Any provision of this Amendment which is
                 ------------
prohibited or unenforceable shall be ineffective to the extent of such
prohibition or unenforceability without invalidating the remaining provisions
hereof in that jurisdiction or affecting the validity or enforceability of such
 provision in any other jurisdiction.

                 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                      -9-
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed this Amendment or
caused it to be executed by their duly authorized officers, all as of the day
and year first above written.

BORROWERS:                              AMERICAN TOWER, L.P., a Delaware limited
                                        partnership

                                        By ATC GP INC., its General Partner

                                        By_____________________________________
                                          Name:  Joseph L. Winn
                                          Title:  Chief Financial Officer

                                        AMERICAN TOWERS, INC., a Delaware
                                        corporation

                                        By:____________________________________
                                           Name:  Joseph L. Winn
                                           Title:  Chief Financial Officer

                                        VERESTAR, INC., a Delaware corporation

                                        By_____________________________________
                                          Name:  Joseph L. Winn
                                          Title:  Chief Financial Officer

                                        TOWERSITES MONITORING, INC., a Delaware
                                        corporation

                                        By_____________________________________
                                          Name:  Joseph L. Winn
                                          Title:  Chief Financial Officer
<PAGE>

Agreed to and Accepted by:

AMERICAN TOWER INTERNATIONAL, INC.,
a Delaware corporation, as a new borrower

By_______________________________
  Name:  Joseph L. Winn
  Title:  Chief Financial Officer<PAGE>

                                                                    Exhibit 10.9

                   NOTICE OF INCREMENTAL FACILITY COMMITMENT

     AMERICAN  TOWERS,  INC., a Delaware  corporation,  AMERICAN TOWER,  L.P., a
Delaware limited partnership, VERESTAR, INC., a Delaware corporation, TOWERSITES
MONITORING, INC., a Delaware corporation and AMERICAN TOWER INTERNATIONAL, INC.,
a Delaware corporation (collectively,  the "Borrowers"), in connection with that
                                            ---------
certain  Amended and Restated Loan Agreement  dated January 6, 2000 (as amended,
modified,  restated or supplemented  from time to time, the "Loan Agreement") by
                                                             --------------
and among the  Borrowers,  the  Lenders  signatory  thereto  (collectively,  the
"Lenders"),  the Issuing Bank (as defined therein) and Toronto Dominion (Texas),
 -------
Inc., as administrative  agent (the  "Administrative Agent"),  hereby certifies
                                      --------------------
that:

         1.    As of the date hereof, the Borrowers have obtained an agreement
to provide an Incremental Facility Commitment in the aggregate amount of two
hundred fifty million and no/100s dollars ($250,000,000.00) from the financial
institutions set forth in Schedule 1 attached hereto in such amounts as set
                          ----------
forth in Schedule 1 attached hereto (collectively, the "Term Loan C
         ----------                                     -----------
Commitments", and individually, a " Term Loan C Commitment"). Within thirty (30)
-----------                         ----------------------
days from the date hereof, financial institutions may provide additional Term
Loan C Commitments provided that, (a) the aggregate amount of all Term Loan C
                   --------
Commitments will not exceed, in the aggregate, THREE HUNDRED MILLION AND NO/100s
DOLLARS ($300,000,000.00), (b) such financial institutions execute a
supplemental signature page to this notice, and (c) no financial institution's
existing Term Loan C Commitment shall be increased or decreased without such
financial institution's consent. At any time an additional Term Loan C
Commitment is provided within the thirty-day period, Schedule 1 hereto will be
modified accordingly and each financial institution's pro rata share of the Term
Loan C Commitment shall be modified accordingly. The terms for repayment of the
loans (the "Term Loan C Loans") made pursuant to the Term Loan C Commitment are
            -----------------
set forth on Schedule 2 attached hereto.
             ----------

         2.    All of the representations and warranties of the Borrowers made
under the Loan Agreement (including, without limitation, all representations and
warranties with respect to the Restricted Subsidiaries) are on the date hereof,
and will be as of the effective date of such Term Loan C Commitment, true and
correct in all material respects after giving effect to any update to
information provided to the Lenders in accordance with the Loan Agreement,
except to the extent previously fulfilled, to the extent subsequently
inapplicable or to the extent that such representations and warranties expressly
relate to an earlier date, in which case such representations and warranties
shall be true and correct on such earlier date.

         3.    There does not exist, on this date, and there will not exist
after giving effect to the Term Loan C Loans, any Default or Event of Default
under the Loan Agreement.

         4.    Set forth on Schedule 3 attached hereto are revised projections
                            ----------
which demonstrate the Borrowers' ability to timely repay the Loans, including
the Term Loan C Loans, and to
<PAGE>

timely comply with the covenants contained in Sections 7.8, 7.9, 7.10 and 7.11
of the Loan Agreement.

         5.    The Lenders having Term Loan C Commitments (the "Term Loan C
                                                                -----------
Lenders") signatory hereto agree that, upon signature hereof, in their capacity
-------
as Term Loan C Lenders, they are bound under the Loan Agreement, as modified by
the terms hereof, as "Lenders" (as defined therein).
                      -------

         6.    This Notice of Incremental Facility Commitment constitutes a Loan
Document. The Loan Agreement shall hereafter be deemed amended and modified as
necessary to incorporate the terms and conditions applicable to the Term Loan C
Commitment which is the subject of this Notice of Incremental Facility
Commitment. The parties hereto agree that the Term Loan C Loans shall be an
"Incremental Facility" as defined in the Loan Agreement.
 --------------------

         Capitalized terms used in this Notice of Incremental Facility
Commitment and not otherwise defined herein are used as defined in the Loan
Agreement.

                 [Remainder of Page Intentionally Left Blank]

                                       2
<PAGE>

         IN WITNESS WHEREOF, the undersigned, acting through an Authorized
Signatory, has signed this Notice of Incremental Facility Commitment on the 26th
day of October, 2001.

BORROWERS:                     AMERICAN TOWERS, INC., a Delaware corporation

                               By:______________________________________________
                                  Name:  Joseph Winn
                                             Chief Financial Officer

                               AMERICAN TOWER, L.P., a Delaware limited
                               partnership

                               By ATC GP Inc., its General Partner

                               By:______________________________________________
                                  Name:  Joseph Winn
                                             Chief Financial Officer

                               VERESTAR, INC., a Delaware corporation

                               By:______________________________________________
                                  Name:  Joseph Winn
                                             Chief Financial Officer

                               TOWERSITES MONITORING, INC., a Delaware
                               corporation

                               By:______________________________________________
                                  Name:  Joseph Winn
                                             Chief Financial Officer

                               AMERICAN TOWER INTERNATIONAL, INC., a
                               Delaware corporation

                               By:______________________________________________
                                  Name:  Joseph Winn
                                             Chief Financial Officer

Affirmation of Guarantors: Each of the Guarantors listed on Schedule 3 attached
                                                            ----------
hereto, by affixing their signature hereto, affirm that the Term Loan C
constitutes an Obligation under the Loan Agreement and the other Loan Documents,
including the Guarantees and that all Collateral pledged by them continues to
secure all of the Obligations (including the Term Loan C Loans) of the
Borrowers, the Restricted Subsidiaries and any other Guarantors.

                               For each of the Guarantors listed on Schedule 3
                               attached hereto:

                               By:______________________________________________
                                  Name:  Joseph Winn
                                  Title:
<PAGE>

LENDERS:                       TORONTO DOMINION (TEXAS), INC., as
                               Administrative Agent and as a Lender

                               By: ____________________________________________
                                   Name: ______________________________________
                                   Title: _____________________________________

                               THE CHASE MANHATTAN BANK, as a Lender

                               By: ____________________________________________
                                   Name: ______________________________________
                                   Title: _____________________________________

                               CREDIT SUISSE FIRST BOSTON, as Lender

                               By: ____________________________________________
                                   Name: ______________________________________
                                   Title: _____________________________________

                               By: ____________________________________________
                                   Name: ______________________________________
                                   Title: _____________________________________

                               GENERAL ELECTRIC CAPITAL CORPORATION, as a Lender

                               By:_____________________________________________
                                  Name: _______________________________________
                                  Title: ______________________________________
<PAGE>

                                  Schedule 1
                                  ----------

                    List of Incremental Facility C Lenders
                    --------------------------------------

Name:                                                       Commitment:
----                                                        ----------
Toronto Dominion (Texas), Inc.                              $75,000,000.00
Credit Suisse First Boston                                  $75,000,000.00
General Electric Capital Corporation                        $50,000,000.00
The Chase Manhattan Bank                                    $50,000,000.00
<PAGE>

                                  Schedule 2
                                  ----------

Incremental
Facility Amount:        Up to $300,000,000 ("Term Loan C")
                                             -----------

Purpose:                Proceeds may used (a) to fund capital expenditures as
                        permitted in the Loan Agreement, (b) to finance
                        acquisitions and investments as permitted in the Loan
                        Agreement, (c) to finance operations of its Restricted
                        Subsidiaries and (d) for general corporate purposes.

Loans:                  The Incremental Facility Lenders having Term Loan C
                        Commitments (the " Term Loan C Lenders") agree
                        severally, and not jointly, upon the terms and subject
                        to the conditions of this Notice and the Loan Agreement
                        to lend to the Borrower, in up to three separate
                        advances, each of which must be at least $100,000,000.00
                        or a multiple thereof, on or from time to time after the
                        effective date of the Term Loan C Commitments, amounts
                        which do not exceed, (i) in the aggregate at any one
                        time outstanding, the Term Loan C Commitments and, (ii)
                        individually, such Term Loan C Lender's Term Loan C
                        Commitment, in each case, as in effect from time to
                        time; provided, however that amounts repaid under the
                              --------  -------
                        Term Loan C Commitments may not be reborrowed.

Conditions Precedent:   The obligation of the Term Loan C Lenders to undertake
                        the Term Loan C Commitments, and the effectiveness of
                        the Term Loan C Commitments are subject to the prior or
                        contemporaneous fulfillment of each of the following
                        conditions:

                              (a)    The Administrative Agent and the Term Loan
                        C Lenders shall have received each of the following:

                                     (i)     Notice of Incremental Facility
                        Commitment, duly executed by the Borrowers, the
                        Restricted Subsidiaries and the other Guarantors;

                                     (ii)    duly executed Term Loan C Notes;

                                     (iii)   all such other documents as either
                        the Administrative Agent or any Term Loan C Lender may
                        reasonably request, certified by an appropriate
                        governmental official or an Authorized Signatory if so
                        requested; and

                                     (iv)    any and all fees which may be due
                        upon closing.
<PAGE>

                              (b)    The Administrative Agent and the Term Loan
                         C Lenders shall have received evidence satisfactory to
                         them that all Necessary Authorizations, including,
                         without limitation, all necessary consents to the
                         closing of this Term Loan C, have been obtained or
                         made, are in full force and effect and are not subject
                         to any pending or, to the knowledge of the Borrowers,
                         threatened reversal or cancellation, and the
                         Administrative Agent and the Term Loan C Lenders shall
                         have received a certificate of an Authorized Signatory
                         so stating.

Availability:            Term Loan C shall be available only after the
                         Administrative Agent shall have received evidence that
                         all amounts under the existing Term Loan A, Term Loan B
                         and the Revolving Loan Commitment are fully drawn.

Incremental Facility C
Maturity Date:           June 30, 2008

Repayment                Term Loan C shall amortize in equal quarterly
Schedule:                installments of 50.0% commencing on March 31, 2008,
                         with the balance due on the Maturity Date as shown
                         above, based on a percentage of the principal balance
                         outstanding under the Term Loan C on March 30, 2008.
                         Such amounts shall be repaid on the last day of each
                         calendar quarter.

Interest Rate:           For all purposes under the Loan Agreement, the Term
                         Loan C shall accrue interest as set forth for the Loans
                         under Section 2.3(f) of the Loan Agreement with the
                         following Applicable Margins:

                                         Base Rate Advance     LIBOR Advance
                         Period          Applicable Margin     Applicable Margin
                         ------          -----------------     -----------------
                         Closing Date through
                         October 31, 2002          3.000%               4.000%

                         November 1, 2002 through
                         March 31, 2003            4.000%               5.000%

                         Thereafter. the Applicable Margins shall increase by
                         0.25% per quarter until the Term Loan C Loans are paid
                         in full.
<PAGE>

Facility Fees:           Commencing on April 1, 2003 and on the first day of
                         each calendar quarter thereafter, a facility fee shall
                         be paid to the Term Loan C Lenders in an amount equal
                         to 0.250% on the Term Loan C commitment. The Facility
                         Fee will be fully earned when due and non-refundable
                         when paid.

Commitment Fee:          A commitment fee shall be paid to the Administrative
                         Agent for the account of each Term Loan C Lender in
                         accordance with such Lender's applicable Commitment
                         Ratio for the Term Loan C based on the average unused
                         Term Loan C Commitment of such Lender for each day from
                         the date hereof through and including the date on which
                         the Term Loan C Commitment is cancelled in full at a
                         rate of two percent (2.000%) per annum. Such commitment
                         fee shall be computed on the basis of a year of 365/366
                         days for the actual number of days elapsed, shall be
                         payable quarterly in arrears on the last Business Day
                         of each calendar quarter, and shall be fully earned
                         when due and non-refundable when paid.

Payments:                Payments of interest and principal shall, except to the
                         extent set forth herein, be payable in the same manner
                         as payments for interest and principal of the Term
                         Loans under the Loan Agreement.

Mandatory Reduction/     (A)Debt Proceeds - 100.0% of the net proceeds from the
Repayment:                  -------------
                         sale of any public or private debt issuance shall be
                         required to repay the Term Loan C and reduce the Term
                         Loan C commitment (to the extent that there are no Term
                         Loan C loans outstanding).

                         (B)Equity Proceeds - 100% of the net proceeds (other
                            ---------------
                         than (x) net proceeds in an amount not to exceed
                         $2,000,000.00 in the aggregate after the Agreement Date
                         from the sale or issuance of Capital Stock in
                         connection with any employee stock option plan of such
                         Person or (y) proceeds received from Capital Stock
                         issued in connection with an Acquisition permitted
                         hereunder) of the sale of any capital stock shall be
                         required to repay the Term Loan C and to reduce the
                         Term Loan C commitment (to the extent that there are no
                         Term Loan C loans outstanding); provided, however, that
                                                         --------  -------
                         on or prior to April 30, 2002, if on the date of any
                         sale of capital stock there are no loans outstanding
                         under Term Loan C, the Term Loan C commitment shall not
                         be reduced by up to $200,000,000 of the net proceeds
                         received from such sale of capital stock.
<PAGE>

                                  Schedule 3
                                  ----------

                                  Guarantors
                                  ----------

ATC Holding, Inc.

American Tower Corporation

ATC Operating, Inc.

OmniAmerica Holdings Corporation

CommSite International, Inc.

TeleCom Towers L.L.C.

ATC LP Inc.

ATS/PCS, LLC

OmniAmerica Towers, Inc.

South Atlantic Tower Corporation

OmniTower, Ltd.

American Tower PA LLC( f.k.a American Tower Texas) (f.k.a. ATC Financing LLC)

ATC Tower Services, Inc. (f.k.a. Specialty Constructors, Inc.)

Commsite Towers, Inc.

US Sitelease, Inc.

Prime Telecom Communications Co.

RFM Facilities Management LP

American Tower Management, Inc.

Maritime Telecommunications Network, Inc.

American Tower Trust #1

American Tower Trust #2

Flash Technology Corporation of America
<PAGE>

Modern Technical Services, Inc.

Flash Technology International, Inc.

Kline Iron & Steel Company, Inc.

ATC (TV), Inc. (f.k.a. Tower Ventures, Inc.)

ATC (TV), LLC, (f.k.a Tower Ventures, LLC)

ATC Midwest, LLC

Verestar Networks, Inc., (f.k.a. InterPacket Networks, Inc.)

Verestar AG, fka Verestar GmBH

Interpacket Promoters India Limited (49%)

Interpacket (Singapore) Pte Limited

Interpacket Brazil Limitada

Interpacket de Argentina S.A. (99%)

Digital Seas International, Inc.

General Telecom, Inc.

Verestar International, Inc.

Unisite, Inc.

American Tower Delaware Corporation

Unistar Technologies, Inc.

Unisite Alpha, Inc.

National Wireless Infrastructure LP

Pisa Real Estate LLC

ATC South LLC

Digital Television Towers, Ltd.

Carolina Towers, Inc.

Site Advantage, Inc.
<PAGE>

MHB Tower Rentals of America, LLC, fka Communisite Tower Rentals of America, LLC

ATC Mexico Holding Corp.

ATC MexHold, Inc.

ATC South America Holding Corp.

MTS Wireless Components (S) PTE, Ltd., a Singapore company

ATC International Holding Corp., (f.k.a American Tower International, Inc.)
(f.k.a. ATC Broadcast GP, Inc.)

American Tower do Brazil, Ltd.

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