Exhibit 10.66A

FIRST AMENDMENT

FIRST AMENDMENT, dated as of July 18, 2008 (this “Amendment”), to the Credit
Agreement, dated as of January 18, 2008 (as amended, supplemented or otherwise
modified from time to time, the “Credit Agreement”), among SBA Senior Finance,
Inc. (the “Borrower”), the several banks and other financial institutions or
entities from time to time parties thereto (the “Lenders”), Toronto Dominion
(Texas) LLC, as administrative agent (in such capacity, the “Administrative
Agent”) and the other agents parties thereto.

W I T N E S S E T H:

WHEREAS, the Borrower, SBA Telecommunications, Inc. (“Holdings”) and SBA
Communications Corporation (the “Parent”) have requested that the Lenders agree
to effect certain modifications to the Credit Agreement as described herein; and

WHEREAS, the Lenders are willing, subject to the terms and conditions set forth
herein, to so amend the Credit Agreement.

NOW THEREFORE, in consideration of the premises and mutual covenants hereinafter
set forth, the parties hereto agree as follows:

Definitions. Unless otherwise defined herein, terms defined in the Credit
Agreement and used herein shall have the meanings given to them in the Credit
Agreement.

Amendment of the Credit Agreement. The Credit Agreement is hereby amended,
effective as of the First Amendment Effective Date (as defined below), as
follows:

Amendments to Section 1.1. Section 1.1 of the Credit Agreement is hereby amended
as follows:

by inserting the following new definitions in appropriate alphabetical order:

“Optasite”: Optasite Holding Company, Inc., or such other entity surviving the
Optasite Merger.

“Optasite Credit Agreement”: the Amended and Restated Credit Agreement, dated
November 2, 2006, by and among Optasite, Inc., Optasite Towers, Morgan Stanley
Asset Funding Inc. and the lenders from time to time parties thereto, as the
same may be amended, supplemented or otherwise modified from time to time.

“Optasite Merger”: the merger of a newly-formed Subsidiary of the Parent or
Holdings with and into Optasite Holding Company, Inc., a Delaware corporation.

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by deleting the final sentence of the definition of Annualized Borrower EBITDA
in its entirety and substituting in lieu thereof the following sentence:

“For purposes of making the computation referred to above, (A) acquisitions that
have been made by the Borrower or any of its Subsidiaries, including through
mergers or consolidations and including any related financing transactions,
during such quarter or subsequent to such quarter and on or prior to such date
of determination shall be deemed to have occurred on the first day of such
quarter and (B) the Consolidated Adjusted EBITDA attributable to Excluded
Subsidiaries, to Optasite and its Subsidiaries (to the extent Optasite and such
Subsidiaries of Optasite are not Guarantors under (and as defined in) the
Guarantee and Collateral Agreement), to discontinued operations, as determined
in accordance with GAAP, and to operations or businesses disposed of prior to
such date of determination, shall be excluded.”

Amendment to Section 6.9. Section 6.9 of the Credit Agreement is hereby amended
as follows:

by deleting the parenthetical in paragraph (a) thereof in its entirety and
substituting in lieu thereof the following parenthetical:

“(other than (w) any leasehold, easement or fee interest in real property,
(x) any Property subject to a Lien expressly permitted by Section 7.3(g),
(y) Property acquired by an Excluded Subsidiary and (z) Property of Optasite and
its Subsidiaries so long as the Optasite Credit Agreement does not permit the
pledge of such Property to the Administrative Agent)”

by deleting the first parenthetical in paragraph (b) thereof in its entirety and
substituting in lieu thereof the following parenthetical:

“(other than (x) an Excluded Subsidiary or (y) Optasite and its Subsidiaries so
long as the Optasite Credit Agreement does not permit, in the case of clauses
(i) and (ii) below, the pledge of the Capital Stock of Optasite and such
Subsidiaries to the Administrative Agent and, in the case of clause (iii) below,
Optasite and such Subsidiaries from becoming parties to the Guarantee and
Collateral Agreement)”

Amendment to Section 8(k). Section 8(k) of the Credit Agreement is hereby
amended by deleting the first parenthetical in each of clauses (iii) and
(iv) thereof in its entirety and in each case substituting in lieu thereof the
following parenthetical:

“(through Subsidiaries that are Guarantors under (and as defined in) the
Guarantee and Collateral Agreement)”

Consent to Amendment of the Guarantee and Collateral Agreement. Pursuant to
Section 10.1 of the Credit Agreement, the Lenders parties hereto hereby consent
to the Administrative Agent entering into an amendment to the Guarantee and
Collateral Agreement in a form acceptable to it in its reasonable discretion in
order to effect the following amendments:

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Amendments to Section 1.1. Section 1.1 of the Guarantee and Collateral Agreement
shall be amended as follows:

by deleting clause (ii) of the definition of Excluded Assets in its entirety and
substituting in lieu thereof the following new clause (ii):

“(ii) Foreign Subsidiary Voting Stock and the shares, stock certificates,
options and rights in respect of the Capital Stock of Optasite and its
Subsidiaries and any Securitization Subsidiary or Excluded Subsidiary, in each
case as excluded from the definition of “Pledged Stock” set forth in this
Section 1.1 and”

by deleting the second proviso to the definition of Pledged Stock in its
entirety and substituting in lieu thereof the following new proviso:

“provided further that “Pledged Stock” shall not include the shares, stock
certificates, options or rights of any nature whatsoever in respect of the
Capital Stock of (i) any Securitization Subsidiary (other than SBA Network
Management, Inc.) or Excluded Subsidiary (other than Excluded Subsidiaries
described in clause (A) of the definition of “Excluded Subsidiaries”) to the
extent the pledge thereof hereunder would not be permitted by Contractual
Obligations of such Securitization Subsidiaries or Excluded Subsidiaries, as
applicable, with Persons who are not Affiliates or (ii) Optasite or any of its
Subsidiaries to the extent the pledge thereof hereunder would not be permitted
by the Optasite Credit Agreement.”

Effectiveness. This Amendment shall become effective as of the date (the “First
Amendment Effective Date”) on which the following conditions have been
satisfied:

The Administrative Agent (or its counsel) shall have received duly executed and
completed counterparts hereof (in the form provided and specified by the
Administrative Agent) that, when taken together, bear the signatures of (x) the
Borrower and (y) the Required Lenders.

To the extent invoiced, the Administrative Agent shall have received payment or
reimbursement of its reasonable out-of-pocket costs and expenses in connection
with this Amendment and any other out-of-pocket costs or expenses of the
Administrative Agent required to be paid or reimbursed pursuant to the Credit
Agreement, including the reasonable fees, charges and disbursements of counsel
for the Administrative Agent.

No Default or Event of Default shall have occurred and be continuing under the
Credit Agreement.

All representations and warranties set forth in Section 4 of the Credit
Agreement shall be true and correct in all material respects, except to the
extent such representations and warranties expressly relate to an earlier date
(in which case such representations and warranties shall have been true and
correct in all material respects as of such earlier date).

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Representations and Warranties. To induce the other parties hereto to enter into
this Amendment, the Borrower hereby represents and warrants to each of the
Lenders that each of the representations and warranties set forth in Section 4
of the Credit Agreement are true and correct in all material respects on and as
of the First Amendment Effective Date with the same effect as though made on and
as of the First Amendment Effective Date, except to the extent such
representations and warranties expressly relate to an earlier date (in which
case such representations and warranties were true and correct in all material
respects as of such earlier date).

Effect of Amendment.

Except as expressly set forth herein, this Amendment shall not by implication or
otherwise limit, impair, constitute a waiver of or otherwise affect the rights
and remedies of the Lenders or the Administrative Agent under the Credit
Agreement or any other Loan Document, and shall not alter, modify, amend or in
any way affect any of the terms, conditions, obligations, covenants or
agreements contained in the Credit Agreement or any other provision of the
Credit Agreement or of any other Loan Document, all of which are ratified and
affirmed in all respects and shall continue in full force and affect. Nothing
herein shall be deemed to entitle the Borrower to a consent to, or a waiver,
amendment, modification or other change of, any of the terms, conditions,
obligations, covenants or agreements contained in the Credit Agreement or any
other Loan Document in similar or different circumstances.

On and after the First Amendment Effective Date, each reference in the Credit
Agreement to “this Agreement”, “hereunder”, “hereof”, “herein”, or words of like
import, and each reference to the Credit Agreement in any other Loan Document
shall be deemed a reference to the Credit Agreement as amended hereby. This
Amendment shall constitute a “Loan Document” for all purposes of the Credit
Agreement and the other Loan Documents.

General.

GOVERNING LAW. THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED AND
INTERPRETED IN ACCORDANCE WITH, THE LAW OF THE STATE OF NEW YORK.

Costs and Expenses. The Borrower agrees to reimburse the Administrative Agent
for its reasonable out-of-pocket costs and expenses in connection with this
Amendment, including the reasonable fees, charges and disbursements of counsel
for the Administrative Agent.

Counterparts. This Amendment may be executed in any number of counterparts and
by different parties hereto in separate counterparts, each of which when so
executed and delivered shall be deemed an original, but all such counterparts
together shall constitute but one and the same instrument. Delivery of any
executed counterpart of a signature page of this Amendment by facsimile or
electronic transmission shall be as effective as delivery of a manually executed
counterpart hereof.

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Headings. The headings of this Amendment are for purposes of reference only and
shall not limit or otherwise affect the meaning hereof.

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

 

SBA SENIOR FINANCE, INC.

By:

 

/s/ Jeffrey A. Stoops

Name:

  Jeffrey A. Stoops

Title:

  President and CEO

TORONTO DOMINION (TEXAS) LLC, as

Administrative Agent

By:

 

/s/ Ian Murray

Name:

  Ian Murray

Title:

  Authorized Signatory TORONTO DOMINION (TEXAS) LLC, as Lender

By:

 

/s/ Ian Murray

Name:

  Ian Murray

Title:

  Authorized Signatory

WACHOVIA BANK, N.A.,

By:

 

/s/ Scott Suddreth

Name:

  Scott Suddreth

Title:

  Vice President

NAME OF LENDER:

LEHMAN COMMERCIAL PAPER, INC.

By:

 

/s/ Ritam Bhalla

Name:

  Ritam Bhalla

Title:

  Authorized Signatory

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NAME OF LENDER:

Citicorp North America, Inc.

By:

 

/s/ Ross Levitsky

Name:

  Ross Levitsky

Title:

  Vice President

NAME OF LENDER:

JPMorgan Chase Bank N.A.

By:

 

/s/ Christophe Vohmann

Name:

  Christophe Vohmann

Title:

  Vice President

NAME OF LENDER:

The Royal Bank of Scotland plc

By:

 

/s/ Scott Webster

Name:

  Scott Webster

Title:

  Managing Director

NAME OF LENDER:

Deutsche Bank Trust Company, Americas

By:

 

/s/ Anca Trifan

Name:

  Anca Trifan

Title:

  Director

By:

 

/s/ Yvonne Tilden

Name:

  Yvonne Tilden

Title:

  Director