<PAGE>

                                                              December 14, 2000
Alamosa PCS, Inc.
200 West Ninth Street Plaza, Suite 102
Wilmington, Delaware 19801

Alamosa PCS Holdings, Inc.
4403 Brownfield Highway
Lubbock, Texas 79407

Attention: David E. Sharbutt

Ladies/Gentlemen:

         Please refer to the Second Amended and Restated Credit Agreement dated
as of June 23, 2000 (the "Credit Agreement") among Alamosa PCS, Inc. (the
"Borrower"), Alamosa PCS Holdings, Inc. ("Holdings"), Texas Telecommunications,
LP, Alamosa Wisconsin Limited Partnership, Alamosa Wisconsin GP, LLC, Alamosa
Delaware GP, LLC, Alamosa Finance LLC, Alamosa Limited LLC, certain financial
institutions (the "Lenders") and Export Development Corporation, as
administrative agent (in such capacity, the "Administrative Agent"). All terms
used but not defined herein shall have the meanings ascribed to such terms in
the Credit Agreement.

         Holdings has advised the Administrative Agent that (i) Holdings has
formed and organized Twenty Holdings, Inc. ("Holdco") and Ten Acquisition, Inc.
("Holdco Sub"), each a Delaware corporation, (ii) Holdco has issued 100 shares
of its common stock to Holdings, with the effect that Holdco became a
wholly-owned subsidiary of Holdings, (iii) Holdco Sub has issued 100 shares of
its common stock to Holdco, with the erect that Holdco Sub became a wholly-owned
subsidiary of Holdco, (iv) Holdco Sub will merge with and into Holdings, with
Holdings being the surviving entity in such merger and (v) the shareholders of
Holdings will receive Capital Stock of Holdco in exchange for their Capital
Stock of Holdings (with such steps in clauses (iv) and (v) occurring
substantially simultaneously, the "Holdco Merger Transaction").

         The Administrative Agent and the Required Lenders hereby (i) consent to
the creation of Holdco and Holdco Sub as Unrestricted Subsidiaries of Holdings
solely for the purpose of effectuating the transactions constituting the Holdco
Merger Transaction; provide that Holdco Sub and, prior to the consummation of
the Holdco Merger Transaction, Holdco shall not incur, create, assume or permit
to exist any Debt; it being understood that upon the consummation of the Holdco
Merger transaction, Holdings will only be subject to the Loan Documents and will
not be subject to the restriction in this proviso as it applies to Holdco Sub;
provided further that

<PAGE>

(x) Holdco shall not be subject to the restriction set forth in clause (m) of
the definition of Unrestricted Subsidiary and (y) Holdco Sub shall not be
subject to the restrictions set forth in clause (k) or (m) of the definition of
Unrestricted Subsidiary, (ii) consent to the Holdco Merger Transaction and the
ownership of Holdings by Holdco as a result of the consummation thereof, (iii)
agree that the Holdco Merger Transaction shall not be deemed to be a Change in
Control and that Holdco shall not be deemed to be a Loan Party under the Credit
Agreement; provided that Holdco shall be a Guarantor under the Credit Agreement,
(iv) waive any non-compliance with Section 9.3 or 9.7 of the Credit Agreement
resulting from the transactions contemplated by the Holdco Merger Transaction
and (v) waive any non-compliance with Section 9.15 of the Credit Agreement
resulting from any amendment or modification of the certificate of incorporation
or other constitutional documents of Holdings to effectuate the transactions
constituting the Holdco Merger Transaction so long as such amendment or
modification could not reasonably be expected to be adverse to the
Administrative Agent or the Lenders.

         In consideration of the foregoing consents and waivers, each Loan Party
acknowledges that if the Holdco Merger Transaction is not consummated on the
date hereof, then such consents and waivers in the foregoing paragraph shall
expire and shall cease to be in effect.

         This letter shall become effective upon the receipt by the
Administrative Agent of (i) counterparts of this letter (or facsimiles thereof)
executed by the Required Lenders and each of the Loan Parties, (ii) a Guaranty
in the form of Exhibit A hereto signed by Holdco, (iii) a Confirmation in the
form of Exhibit B hereto signed by each of the Loan Parties, (iv) resolutions of
the board of directors of Holdco authorizing the execution, delivery and
performance by Holdco of the Guaranty, certified by the Secretary or an
Assistant Secretary of Holdco, (v) a certificate of incumbency certified by the
Secretary or an Assistant Secretary of Holdco certifying as to the name of each
officer or other representative of Holdco (A) who is authorized to sign the
Guaranty, together with specimen signatures of each such officer or other
representative, and (B) who will, until replaced by other officers or
representative duly authorized for that purpose, act as its representative for
the purposes of signing documents and giving notices and other communications in
connection with the Guaranty and the transactions contemplated thereby, (vi) the
certificate of incorporation or articles of incorporation of Holdco certified by
the Secretary or Assistant Secretary, (vii) the bylaws of Holdco certified by
its Secretary or an Assistant Secretary, (viii) a certificate of the Secretary
of State of the State of Delaware as to the existence and good standing of
Holdco, (ix) an opinion of Skadden, Arps, Slate, Meagher & Flom LLP, counsel to
Holdco substantially in the form of Exhibit C hereto, (x) the Agreement and Plan
of Merger among Holdings, Holdco and Holdco Sub evidencing the Holdco Merger
Transaction and (xi) such other documents as the Administrative Agent may
reasonably request.

         Holdings agrees to provide to the Administrative Agent, within five
business days of the consummation of the Holdco Merger Transaction, (i) a
file-stamped acknowledgment copy of the Agreement and Plan of Merger from the
Secretary of State of the State of Delaware, (ii) the certificate of
incorporation of Holdco reflecting a change in the name of Holdco to "Alamosa

                                        2
<PAGE>

PCS Holdings, Inc." and (iii) the certificate of incorporation of Holdings
reflecting, among other things, a change in the name of Holdings to "Alamosa
(Delaware), Inc."

         This letter is limited to the matters specifically set forth herein and
shall not be deemed to constitute a waiver or consent with respect to any other
matter whatsoever. Except as specifically set forth herein, the Credit Agreement
shall remain in full force and effect and is hereby ratified in all respects.
This letter may be executed in counterparts and by the parties hereto on
separate counterparts.

         This letter shall be governed by and construed in accordance with the
internal laws of the State of New York (without regard to conflicts of laws
principles other than Section 5-1401 of the New York General Obligations Law).

         Please acknowledge your agreement to the foregoing by signing and
returning a counterpart hereof to the Administrative Agent.

                      [SIGNATURE PAGES BEGIN ON NEXT PAGE]

                                        3
<PAGE>

                                       EXPORT DEVELOPMENT
                                       CORPORATION, as Administrative Agent
                                       and as a Lender

                                       By: /s/ Robert Kelly
                                          --------------------------------------
                                       Name: Robert Kelly
                                            ------------------------------------
                                       Title: Financial Services Manager
                                             -----------------------------------

                                       By: /s/ Stephen Davies
                                          --------------------------------------
                                       Name: Stephen Davies
                                            ------------------------------------
                                       Title: Financial Services Manager
                                             -----------------------------------

ACCEPTED AND AGREED:

ALAMOSA PCS, INC.

By: /s/ David Sharbutt
   ----------------------------------------
Name: David Sharbutt
     --------------------------------------
Title: President
      -------------------------------------

ALAMOSA PCS HOLDINGS, INC.

By: /s/ David Sharbutt
   ----------------------------------------
Name: David Sharbutt
     --------------------------------------
Title: Chairman and Chief Executive Officer
      -------------------------------------

TEXAS TELECOMMUNICATION, LP

By:    Alamosa Delaware GP, LLC
Title: General Partner

By: /s/ David Sharbutt
   ----------------------------------------
Name: David Sharbutt
     --------------------------------------
Title: Manager and President
      -------------------------------------

                                      S-1
<PAGE>

ALAMOSA WISCONSIN LIMITED PARTNERSHIP

By:    Alamosa Wisconsin GP, LLC
Title: General Partner

By: /s/ David Sharbutt
   --------------------------------------
Name: David Sharbutt
     ------------------------------------
Title: Manager and President
      -----------------------------------

ALAMOSA DELAWARE GP, LLC

By: /s/ David Sharbutt
   --------------------------------------
Name: David Sharbutt
     ------------------------------------
Title: Manager and President
      -----------------------------------

ALAMOSA WISCONSIN GP, LLC

By: /s/ David Sharbutt
   --------------------------------------
Name: David Sharbutt
     ------------------------------------
Title: Manager and President
      -----------------------------------

ALAMOSA FINANCE, LLC

By: /s/ David Sharbutt
   --------------------------------------
Name: David Sharbutt
     ------------------------------------
Title: Manager and President
      -----------------------------------

ALAMOSA LIMITED, LLC

By: /s/ Barry Crozier
   --------------------------------------
Name: Barry Crozier
     ------------------------------------
Title: Vice President
      -----------------------------------

                                       S-2