<PAGE>


                                                                  Exhibit 10.55

                                                                 EXECUTION COPY


                           FOURTH AMENDMENT AND WAIVER dated as of August 6,
                  2001 (this "Amendment"), to the Amended and Restated Credit
                  Agreement, dated as of February 14, 2001, as amended and
                  restated as of March 30, 2001, as heretofore amended (the
                  "Credit Agreement"), among ALAMOSA HOLDINGS, INC.
                  ("Superholdings"), ALAMOSA (DELAWARE), INC. ("Alamosa
                  Delaware"), ALAMOSA HOLDINGS, LLC (the "Borrower" and,
                  together with Superholdings and Alamosa Delaware, the "Alamosa
                  Parties"), the Lenders party thereto (the "Lenders"), EXPORT
                  DEVELOPMENT CORPORATION, as Co-Documentation Agent, FIRST
                  UNION NATIONAL BANK, as Documentation Agent, TORONTO DOMINION
                  (TEXAS), INC., as Syndication Agent, and CITICORP USA, INC.,
                  as Administrative Agent and Collateral Agent (the "Agent").

                  WHEREAS the Alamosa Parties have requested that certain
provisions of the Credit Agreement be amended and waived in the manner provided
for in this Amendment, and the Required Lenders are willing to agree to such
amendments and waiver on the terms and conditions hereinafter set forth;


                  NOW, THEREFORE, the parties hereto hereby agree as follows:

                  1. Defined Terms. Capitalized terms used and not defined
herein shall have the meanings given to them in the Credit Agreement, as amended
hereby.

                  2.  Amendments to Credit Agreement.
                      -------------------------------
(a) Section 1.01 of the Credit Agreement is hereby amended by (i) amending and
restating in its entirety each of the definitions set forth below:

                           "'Alamosa Delaware Indentures' means (i) the
                             ---------------------------
         12 7/8% Senior Discount Notes Indenture, (ii) the 12 1/2% Senior Notes
         Indenture and (iii) the New Senior Notes Indenture."

                           "'Revolving Commitment' means, with respect to each
         Lender, the commitment, if any, of such Lender to make Revolving Loans
         and to acquire participations in Letters of Credit, expressed as an
         amount representing the maximum aggregate amount of such Lender's
         Revolving Exposure hereunder, as such commitment may be (a) reduced
         from time to time pursuant to Section 2.07 and (b) reduced or increased
         from time to time pursuant to assignments by or to such Lender pursuant
         to Section 9.04. The initial amount of


<PAGE>



                                                                              2

         each Lender's Revolving Commitment is set forth on Schedule 2.01, or in
         the Assignment and Acceptance pursuant to which such Lender shall have
         assumed its Revolving Commitment, as applicable. The aggregate amount
         of the Lenders' Revolving Commitments is $25,000,000."

                           "'Term Commitment' means, with respect to each
         Lender, the commitment, if any, of such Lender to make a Term Loan
         hereunder, expressed as an amount representing the maximum principal
         amount of the Term Loan to be made by such Lender hereunder, as such
         commitment may be (a) reduced from time to time pursuant to Section
         2.07 and (b) reduced or increased from time to time pursuant to
         assignments by or to such Lender pursuant to Section 9.04. The initial
         amount of each Lender's Term Commitment is set forth on Schedule 2.01,
         or in the Assignment and Acceptance pursuant to which such Lender shall
         have assumed its Commitment, as applicable. The aggregate amount of the
         Lenders' Term Commitments is $200,000,000."

         (ii) adding the following new definitions in appropriate alphabetical
order:

                           "'New Senior Notes Indenture' means the indenture
         under which the Senior Notes are issued and all other instruments,
         agreements and other documents evidencing or governing the Senior Notes
         or providing for any Guarantee or other right in respect thereof."

                           "'Senior Notes' means the Senior Notes due 2011 of
         Alamosa Delaware issued in August 2001 in a single issuance and in an
         aggregate principal amount not in excess of $200,000,000."

                  (b) Section 6.01(a) of the Credit Agreement is hereby amended
by deleting the word "and" at the end of clause (xiii), replacing the period at
the end of clause (xiv) with "; and" and inserting a new clause (xv) as follows:

                  "(xv) the Senior Notes in an aggregate principal amount not in
         excess of $200,000,000 (and the related Guarantees) and extensions,
         renewals and replacements thereof that do not increase the outstanding
         principal amount thereof or result in an earlier maturity date or
         decreased weighted average life thereof; provided that the Senior Notes
         have a market rate of interest determined at the time of their pricing,
         the Senior Notes do not have any scheduled amortization prior to


<PAGE>



                                                                              3

         the date that is six months after the Term Maturity Date, and the terms
         and conditions of the Senior Notes and the New Senior Notes Indenture
         (including with respect to covenants and Guarantees) are otherwise
         substantially the same as those of the 12 1/2% Senior Notes and 12 1/2%
         Senior Notes Indenture (except with respect to the interest escrow
         account permitted under Section 6.02(a)(viii))."

                  (c) Section 6.02(a) of the Credit Agreement is hereby amended
by deleting the word "and" at the end of clause (vi), replacing the period at
the end of clause (vii) with "; and " and inserting a new clause (viii) as
follows:

                  "(viii) Liens on cash and cash equivalents in connection with
         an interest escrow account securing obligations in respect of the
         Senior Notes, provided that (A) such account is established at the time
         of issuance of the Senior Notes and (B) such Liens extend only to Net
         Proceeds of such issuance deposited in such account in an amount not
         exceeding the amount of the initial four semiannual interest payments
         on the Senior Notes, and to earnings thereon and proceeds thereof."

                  (d) Clause (iv) of Section 6.08(a) of the Credit Agreement is
hereby amended by inserting the words "the Senior Notes," immediately prior to
the words "the 12 7/8% Senior Discount Notes".

                  (e) Clause (v) of Section 6.08(b) of the Credit Agreement is
hereby amended and restated in its entirety as follows:

                  "(v) the exchange, in a registered public offering, for the 12
         1/2% Senior Notes or the Senior Notes, as the case may be, of senior
         notes of Alamosa Delaware in an equivalent principal amount having the
         same terms and conditions as the 12 1/2% Senior Notes or the Senior
         Notes, as applicable;".

                  (f) Section 6.10 of the Credit Agreement is hereby amended by
inserting the words "the New Senior Notes Indenture," immediately prior to the
words "the 12 7/8% Senior Discount Notes Indenture" in clause (ii)(B) of the
first proviso in such Section.

                  (g) Schedule 2.01 to the Credit Agreement is hereby replaced
by Schedule 2.01 attached hereto.

                  3.  Waiver.  Each of the undersigned Lenders
hereby expressly waives compliance by the Borrower with the


<PAGE>



                                                                             4

notice requirement set forth in Section 2.07(d) with respect to the Borrower's
voluntary reduction of the Revolving Commitments and the Term Commitments as set
forth herein.

                  4.  Consent. After giving effect to this Amendment, and the
prepayments of Term Loans and reductions in Commitments provided for herein, the
aggregate principal amounts of Roberts Term Loans, Southwest Term Loans and WOW
Term Loans shall be reduced to zero.

                  5.  Effect of Amendments and Waiver. 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 or remedies of
the Lenders, the Collateral Agent, the Syndication Agent, the Co-Documentation
Agent, the Documentation Agent or the Administrative Agent under the Credit
Agreement, as amended by this Amendment, or under 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, as amended by this Amendment, or any other Loan Document, all of
which are ratified and affirmed in all respects and shall continue in full force
and effect. Nothing herein shall be deemed to entitle the Alamosa Parties 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, as amended by this Amendment, or any other Loan Document in similar
or different circumstances. This Amendment shall apply and be effective only
with respect to the provisions of the Credit Agreement expressly referred to
herein. After the date hereof, any reference to the Credit Agreement shall mean
the Credit Agreement as modified hereby. This Amendment shall constitute a "Loan
Document" for all purposes of the Credit Agreement and the other Loan Documents.

                  6.  Representations and Warranties.  Each of the
Alamosa Parties hereby represents and warrants to the Agent and the Lenders as
of the date hereof as follows:

                  (a) No Default or Event of Default has occurred and is
continuing.

                  (b) The execution, delivery and performance by the Alamosa
Parties of this Amendment have been duly authorized by all necessary corporate
and other action and do not and will not require any registration with, consent
or approval of, notice to or action by, any person (including any governmental
agency) in order to be effective and enforceable. The Credit Agreement as
amended by this

<PAGE>



                                                                             5

Amendment constitutes the legal, valid and binding obligation of each of the
Alamosa Parties, enforceable against it in accordance with its terms, subject to
applicable bankruptcy, insolvency, reorganization, moratorium or other laws
affecting creditors' rights generally and subject to general principles of
equity, regardless of whether considered in a proceeding in equity or at law.

                  (c) All representations and warranties of the Alamosa Parties
contained in Article III of the Credit Agreement (other than representations or
warranties expressly made only on and as of the Restatement Effective Date) are
true and correct in all material respects as of the date hereof.

                  7.  Effectiveness.  This Amendment shall become
effective (the "Amendment Effective Date") only upon satisfaction of the
following conditions prior to 10:00 a.m., Eastern Standard Time, on August 20,
2001:
                  (i) the Agent shall have received counterparts hereof duly
         executed and delivered by the Alamosa Parties and the Required Lenders;

                   (ii) Alamosa Delaware shall have received gross cash proceeds
         from the issuance of the Senior Notes of at least $146,000,000 and
         shall have contributed to the Borrower the entire Net Proceeds thereof
         less an amount equal to the initial four semiannual interest payments
         on the Senior Notes, which amount shall have been placed in an interest
         reserve escrow account in connection with the issuance of, and to
         secure Alamosa Delaware's obligations under, the Senior Notes;

             (iii) the Borrower shall have prepaid Term Loans
         ratably in an aggregate principal amount of at least
         $64,400,000;

             (iv) to the extent Alamosa Delaware receives gross cash proceeds in
         excess of $150,000,000 from the issuance of Senior Notes, (A) the
         Borrower shall have applied the Net Proceeds in respect of such excess
         (less escrowed interest in respect of such excess as contemplated by
         clause (ii) above) to prepay Term Loans and permanently reduce Term
         Commitments ratably and in amounts determined by the Administrative
         Agent to be substantially proportionate to the Term Loans and Term
         Commitments existing immediately prior to the Amendment Effective Date;
         and (B) the Revolving Commitments shall be permanently reduced in an
         amount equal to any

<PAGE>



                                                                              6

         remaining Net Proceeds (less such escrowed interest) after application
         thereof pursuant to clause (A) less an amount equal to the reduction in
         Term Commitments required pursuant to clause (A); and

                  (v) the Agent shall have received evidence reasonably
         satisfactory to it that, as of the Amendment Effective Date, Total
         Borrower Capital is equal to at least $625,931,000 plus the amount
         contributed to the Borrower pursuant to clause (ii) above.

                  8.   Expenses.  The Alamosa Parties, jointly and
severally, agree to reimburse the Agent for its out-of-pocket expenses in
connection with this Amendment, including the reasonable fees, charges and
disbursements of Cravath, Swaine & Moore, counsel for the Agent.

                  9. GOVERNING LAW; COUNTERPARTS. (A) THIS AMENDMENT AND THE
RIGHTS AND OBLIGATIONS OF THE PARTIES HERETO SHALL BE GOVERNED BY AND CONSTRUED
IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

                  (b) This Amendment may be executed in any number of
counterparts and by different parties hereto on separate counterparts, each of
which when so executed and delivered shall be deemed an original, but all of
which together shall constitute a single instrument. Delivery of an executed
counterpart of a signature page of this Amendment by facsimile transmission
shall be as effective as delivery of a manually executed counterpart hereof.


<PAGE>



                                                                            7


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


                                              ALAMOSA HOLDINGS, INC.,

                                                by
                                                    /s/ Kendall W. Cowan
                                                   ----------------------
                                                   Name:
                                                   Title:


                                              ALAMOSA (DELAWARE), INC.,

                                                by
                                                    /s/ Kendall W. Cowan
                                                   ----------------------
                                                   Name:
                                                   Title:


                                             ALAMOSA HOLDINGS, LLC,

                                               by
                                                   /s/ Kendall W. Cowan
                                                  ----------------------
                                                  Name:
                                                  Title:


                                           CITICORP USA, INC., individually and
                                           as Administrative Agent,


                                             by
                                                  /s/ John P. Judge
                                                 ------------------------
                                                  Name: John P. Judge
                                                  Title: Vice President



<PAGE>



                                                                             8

                                                               SIGNATURE PAGE to
                                                    FOURTH AMENDMENT AND WAIVER,
                                                      dated as of August 6, 2001
                                                        to ALAMOSA HOLDINGS, LLC
                                           AMENDED AND RESTATED CREDIT AGREEMENT






                        To approve the Fourth Amendment and Waiver:


                        Name of Institution: Bank of Novia Scotia
                                            -----------------------------

                                         by /s/Stephen C. Levi
                                            -------------------
                                            Name: Stephen C. Levi
                                            Title: Authorized Signatory




<PAGE>



                                                                             9

                                                              SIGNATURE PAGE to
                                                   FOURTH AMENDMENT AND WAIVER,
                                                     dated as of August 6, 2001
                                                       to ALAMOSA HOLDINGS, LLC
                                          AMENDED AND RESTATED CREDIT AGREEMENT






                    To approve the Fourth Amendment and Waiver:


                    Name of Institution:  CoBank ACB
                                         --------------------------------

                                       by /s/ Anita Youngblut
                                          -------------------------------
                                          Name: Anita Youngblut
                                          Title: Vice President




<PAGE>



                                                                            10

                                                             SIGNATURE PAGE to
                                                  FOURTH AMENDMENT AND WAIVER,
                                                    dated as of August 6, 2001
                                                      to ALAMOSA HOLDINGS, LLC
                                         AMENDED AND RESTATED CREDIT AGREEMENT




                  To approve the Fourth Amendment and Waiver:


                  Name of Institution: Export Development Corporation
                                      --------------------------------------

                                     by /s/ Luisa Rebolledo
                                        ------------------------------------
                                        Name: Luisa Rebolledo
                                        Title: Loan Asset Manager


                                     by /s/ Vito Di Turi
                                        ------------------------------------
                                        Name: Vito Di Turi
                                        Title: Loan Asset Manager


<PAGE>



                                                                            11

                                                             SIGNATURE PAGE to
                                                  FOURTH AMENDMENT AND WAIVER,
                                                    dated as of August 6, 2001
                                                      to ALAMOSA HOLDINGS, LLC
                                         AMENDED AND RESTATED CREDIT AGREEMENT






                  To approve the Fourth Amendment and Waiver:


                  Name of Institution: First Union National Bank
                                       ---------------------------------

                                      by /s/ Stephen G. Locke
                                         ---------------------
                                         Name: Stephen G. Locke
                                         Title: Asst. Vice President




<PAGE>



                                                                            12

                                                             SIGNATURE PAGE to
                                                  FOURTH AMENDMENT AND WAIVER,
                                                    dated as of August 6, 2001
                                                      to ALAMOSA HOLDINGS, LLC
                                           AMENDED AND RESTATED CREDIT AGREEMENT





                      To approve the Fourth Amendment and Waiver:


                      Name of Institution: Fortis Capital Corp.
                                           --------------------------------

                                         by /s/ Alan E. McLintock
                                            -------------------------------
                                            Name: Alan E. McLintock
                                            Title: Managing Director

                                         by /s/ Colm Kelly
                                            -------------------------------
                                            Name: Colm Kelly
                                            Title: Assistant Vice President



<PAGE>



                                                                           13

                                                              SIGNATURE PAGE to
                                                   FOURTH AMENDMENT AND WAIVER,
                                                     dated as of August 6, 2001
                                                       to ALAMOSA HOLDINGS, LLC
                                        AMENDED AND RESTATED CREDIT AGREEMENT






             To approve the Fourth Amendment and Waiver:


             Name of Institution: IBM Credit Corporation
                                 -------------------------------------------

                                by /s/ Salvatore F. Grosso
                                  ------------------------------------------
                                  Name: Salvatore F. Grosso
                                  Title: Manager, Commercial
                                         Financing Americas




<PAGE>



                                                                             14

                                                             SIGNATURE PAGE to
                                                  FOURTH AMENDMENT AND WAIVER,
                                                    dated as of August 6, 2001
                                                      to ALAMOSA HOLDINGS, LLC
                                         AMENDED AND RESTATED CREDIT AGREEMENT






                 To approve the Fourth Amendment and Waiver:


                 Name of Institution:  Societe Generale
                                      ---------------------------------

                                   by /s/ Mark Vigil
                                      ---------------------------------
                                      Name: Mark Vigil
                                      Title: Director




<PAGE>



                                                                           15

                                                             SIGNATURE PAGE to
                                                  FOURTH AMENDMENT AND WAIVER,
                                                    dated as of August 6, 2001
                                                      to ALAMOSA HOLDINGS, LLC
                                         AMENDED AND RESTATED CREDIT AGREEMENT






                   To approve the Fourth Amendment and Waiver:


                   Name of Institution: Toronto Dominion (Texas), Inc.
                                       ----------------------------------

                                     by /s/ Alva J. Jones
                                       ----------------------------------
                                       Name: Alva J. Jones
                                       Title: Vice President




<PAGE>



                                                                           16

                                                             SIGNATURE PAGE to
                                                  FOURTH AMENDMENT AND WAIVER,
                                                    dated as of August 6, 2001
                                                      to ALAMOSA HOLDINGS, LLC
                                         AMENDED AND RESTATED CREDIT AGREEMENT






                    To approve the Fourth Amendment and Waiver:

                                         Westdeutsche Landesbank
                    Name of Institution: Girozentrale, New York Branch
                                        ----------------------------------

                                      by /s/ Peter Stevenson
                                        ----------------------------------
                                         Name: Peter Stevenson
                                         Title: Director

                                      by /s/ David Yu
                                        ----------------------------------
                                        Name: David Yu
                                        Title: Associate Director



<PAGE>


                                                                            17


                                                                 SCHEDULE 2.01




ALAMOSA HOLDINGS, LLC
$225,000,000 SENIOR SECURED CREDIT FACILITIES

<TABLE>
<CAPTION>


                          LENDER                               REVOLVING CREDIT             TERM LOAN
                          ------                               ----------------             ---------
<S>                                                                <C>                      <C>
Citicorp USA, Inc.                                                   $2,861,201.32            $19,077,458.03
Toronto Dominion (Texas), Inc.                                       $3,064,123.37            $22,442,633.44
Export Development Corporation                                       $2,840,909.09            $20,807,739.61
First Union National Bank                                            $2,435,064.93            $17,835,205.38
The Bank of Nova Scotia                                              $2,435,064.93            $17,835,205.38
Fortis Capital Corp.                                                 $2,435,064.93            $17,835,205.38
CoBank, ACB                                                          $2,029,220.78            $14,862,671.15
General Electric Capital Corporation                                 $2,029,220.78            $14,862,671.15
Societe Generale                                                     $2,029,220.78            $14,862,671.15
Westdeutsche Landesbank Girozentrale, New York                       $2,029,220.78            $14,862,671.15
Branch
Franklin Floating Rate Trust*                                                    -            $13,513,513.51
IBM Credit Corporation                                                 $811,688.31             $5,945,068.46
Oppenheimer Senior Floating Rate Fund*                                           -             $3,568,097.02
Franklin Floating Rate Master Series*                                            -             $1,689,189.19
----------------------------------------------------------- ----------------------  ------------------------
TOTAL COMMITMENTS                                                   $25,000,000.00           $200,000,000.00

*Fully Funded

</TABLE>