<PAGE>

                                                                   Exhibit 10.21

                                    FORM OF
                      AMENDMENT NO. 1 TO THE FIRST AMENDED
                      AND RESTATED STOCKHOLDERS' AGREEMENT

         AMENDMENT NO. 1 TO THE FIRST AMENDED AND RESTATED STOCKHOLDERS'
AGREEMENT ("Amendment No. 1") dated as of April 4, 2002, by and among AT&T
            ---------------
WIRELESS PCS LLC, a Delaware limited liability company (together with its
Affiliated Successors (as hereinafter defined), "AT&T PCS"), the investors
                                                 --------
listed under the heading "Cash Equity Investors" on the signature pages hereto
(individually, each a "Cash Equity Investor" and, collectively, with any of
                       --------------------
their respective Affiliated Successors, the "Cash Equity Investors"), the
                                             ---------------------
individuals listed under the heading "Management Stockholders" on the signature
pages hereto (individually, each a "Management Stockholder" and, collectively,
                                    ----------------------
the "Management Stockholders"), the individuals listed under the heading
     -----------------------
"Independent Directors" on the signature pages hereto (individually, each an
"Independent Director" and, collectively, the "Independent Directors") and
 --------------------                          ---------------------
TRITON PCS HOLDINGS, INC., a Delaware corporation (the "Company"). Certain
                                                        -------
capitalized terms used herein and not otherwise defined have the meaning
assigned to such term in the Stockholders' Agreement referred to below.

         WHEREAS, each of the parties hereto (other than the Company) are
Stockholders of the Company;

         WHEREAS, the parties hereto are parties to that certain First Amended
and Restated Stockholders' Agreement, dated as of October 27, 1999 (the
"Stockholders' Agreement"), pursuant to which, among things, the parties hereto
 -----------------------
entered into certain agreements regarding the operation of the Company's
business;

         WHEREAS, AT&T PCS, the Company and Triton PCS License Company L.L.C., a
Delaware limited liability company and an indirect wholly-owned subsidiary of
the Company ("Triton License Company" and, collectively with the Company,
              ----------------------
"Triton"), are parties to that certain Exchange and Acquisition Agreement, dated
 ------
as of November 15, 2001 (the "Exchange and Acquisition Agreement"), pursuant to
                              ----------------------------------
which, among other things, effective upon the closing of the transactions
contemplated by the Exchange and Acquisition Agreement (the "Exchange and
                                                             ------------
Acquisition Closing"), Triton License Company will acquire from AT&T PCS a 20
-------------------
MHz A Block PCS license covering the entirety of Bulloch and Screven Counties,
Georgia within the Atlanta, Georgia MTA (the "Assigned Atlanta License"), as
                                              ------------------------
more fully described, and upon the terms set forth, therein; and

         WHEREAS, pursuant to the Exchange and Acquisition Agreement it was
agreed, and the Company and AT&T PCS desire, that, effective upon the Exchange
and Acquisition Closing (which is occurring as of the date hereof), (A) the
Stockholders' Agreement be amended to provide that the terms "Business" and "PCS
Territory", each as used in the Stockholders' Agreement, be amended to include
Bulloch and Screven Counties, Georgia (the "Assigned Markets") and (B) Schedule
                                            ----------------
V to the Stockholders' Agreement be amended to include the build-out plan for
the Assigned Markets.

<PAGE>

         NOW THEREFORE, in consideration of the mutual promises and covenants
contained herein and in the Exchange and Acquisition Agreement and for other
good and valuable consideration the receipt and sufficiency of which is hereby
acknowledged, the parties hereby agree as follows:

         1.   Amendments.  From and after the later to occur of (x) the
              ----------
Amendment Effectiveness Date (as defined herein), and (y) the Exchange and
Acquisition Closing, without any further action on the part of the parties
hereto, the following amendments to the Stockholders' Agreement shall be
effective and in full force and effect;

              (i)    Schedule VI to the Stockholders' Agreement (PCS Territory),
         shall be amended to include Bulloch and Screven Counties in the portion
         of the PCS Territory within Savannah, GA set forth in Item IV therein;

              (ii)   Schedule XII to the Stockholders' Agreement shall be
         amended to include "the 20 MHz PCS License for Bulloch County, GA and
         Screven County, GA within the Atlanta MTA acquired by the Company
         pursuant to the Exchange and Acquisition Agreement dated as of November
         15, 2001"; and

              (iii)  Schedule V to the Stockholders' Agreement shall be amended
         to include the build-out plan, set forth in Exhibit A hereto, for the
         Assigned Markets.

         2.   Amendment Effectiveness Date.  This Amendment No. 1 shall be
              ----------------------------
effective on the date that a counterpart hereof shall have been executed by each
of the Company, AT&T PCS, holders of 66 2/3% of the Common Stock Beneficially
Owned by the Cash Equity Investors and holders of 60.1% of the Common Stock
Beneficially Owned by the Management Stockholders (the "Amendment Effectiveness
                                                        ------------------------
Date").
----

         3.   Representation and Warranties.
              -----------------------------

         (a)  Each of the Company, as to itself, each Cash Equity Investor, as
to itself, and AT&T PCS, as to itself, represents and warrants, as applicable,
to each of the other parties as follows:

              (i)    It is a corporation, limited liability company, general
         partnership or limited partnership, duly organized, validly existing
         and in good standing under the laws of its jurisdiction of organization
         and has the requisite power and authority to own, lease and operate its
         properties and to carry on its business as now being conducted.

              (ii)   It has the requisite power, authority and capacity to
         execute, deliver and perform this Amendment No. 1.

              (iii)  The execution and delivery of this Amendment No. 1 by it
         have been duly and validly authorized by its Board of Directors (or
         equivalent body), if required, and no other proceedings on its part
         which have not been taken (including, without limitation, approval of
         its stockholders, partners or members, as applicable) are necessary to
         authorize this Amendment No. 1.

                                       2

<PAGE>

              (iv)   This Amendment No. 1 has been duly executed and delivered
         by it and constitutes its valid and binding obligation, enforceable
         against it in accordance with its terms, except as such enforceability
         may be limited by bankruptcy, insolvency, moratorium or other similar
         laws affecting or relating to enforcement of creditors' rights
         generally and may be subject to general principles of equity.

              (v)    The execution, delivery and performance by it of this
         Amendment No. 1 will not (A) conflict with, or result in a breach or
         violation of, any provision of its organizational documents; (B)
         constitute, with or without the giving of notice or passage of time or
         both, a breach, violation or default, create a Lien, or give rise to
         any right of termination, modification, cancellation, prepayment or
         acceleration, under (x) any Law or License, or (y) any note, bond,
         mortgage, indenture, lease, agreement or other instrument, in each case
         which is applicable to or binding upon it or any of its assets; or (c)
         require any Consent, or the approval of its board of directors, general
         partner, stockholders or similar constituent bodies, as the case may be
         (which approvals have been obtained), except in each case, where such
         breach, violation, default, Lien, right, or the failure to obtain or
         give such Consent would not have a material adverse effect on it or its
         ability to perform its obligations hereunder.

              (vi)   There is no action, proceeding or investigation pending or,
         to its knowledge, threatened against it or any of its properties or
         assets that would be reasonably expected to have a material adverse
         effect on its ability to enter into this Amendment No. 1 or to fulfill
         its obligations hereunder.

         (b)  Each Management Stockholder that has executed this Amendment No. 1
represents and warrants, as to himself or herself, to each of the other parties
as follows:

              (i)    He or she has the requisite capacity to execute, deliver
         and perform this Amendment No. 1.

              (ii)   This Amendment No. 1 has been duly executed and delivered
         by him or her and constitutes his or her valid and binding obligation,
         enforceable against him or her in accordance with its terms, except as
         such enforceability may be limited by bankruptcy, insolvency,
         moratorium or other similar laws affecting or relating to enforcement
         of creditors' rights generally and may be subject to general principles
         of equity.

              (iii)  The execution, delivery and performance by him or her of
         this Amendment No. 1 will not require any Consent, except in each case,
         where the failure to obtain or give such Consent would not have a
         material adverse effect on his or her ability to perform his or her
         obligations hereunder.

              (iv)   There is no action, proceeding or investigation pending or,
         to the knowledge of him or her, threatened against him or her or any of
         his or her properties or assets that would be reasonably expected to
         have a material adverse

                                       3

<PAGE>

         effect on his or her ability to enter into this Amendment No. 1 or to
         fulfill his or her respective obligations hereunder.

         4.   Severability of Provisions. Any provision of this Amendment No. 1
              --------------------------
which is prohibited or unenforceable in any jurisdiction shall, as to such
jurisdiction, be ineffective to the extent of such prohibition or
unenforceability without invalidating the remaining provisions hereof or
affecting the validity or remaining provisions hereof or affecting the validity
or enforceability of such provision in any other jurisdiction.

         5.   Agreements to Remain in Full Force and Effect.  This Amendment No.
              ---------------------------------------------
1 shall be deemed to be an amendment to the Stockholders' Agreement. All
references to the Stockholders' Agreement in any other agreements or documents
shall on and after the date hereof be deemed to refer to the Stockholders'
Agreement as amended hereby. Except as amended hereby, the Stockholders'
Agreement shall remain in full force and effect and is hereby ratified, adopted
and confirmed in all respects.

         6.   Heading.  The headings in this Amendment No. 1 are inserted for
              -------
convenience and identification only and are not intended to describe, interpret,
define or limit the scope, extent or intent of this Amendment No. 1 or any
provision thereof.

         7.   Counterparts.  This Amendment No. 1 may be executed in
              ------------
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same Agreement.

         8.   Governing Law.  This Amendment No. 1 shall be governed and
              -------------
construed in accordance with the laws of the State of Delaware.

                                       4