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                                                                     Exhibit 4.4


                      AMENDMENT NO. 3 TO THE THIRD AMENDED
                      AND RESTATED STOCKHOLDERS' AGREEMENT


     Amendment  No. 3,  dated as of March 31,  2001,  to the Third  Amended  and
Restated  Stockholders'  Agreement,  dated as of April 20,  1999,  as amended by
Amendment No. 1, dated as of November 20, 2000, and Amendment No. 2, dated as of
December 14, 2000 (collectively,  the "Stockholders'  Agreement"),  by and among
the Company, the WCAS Purchasers,  SBCT, TPC, CIBC II, CIBC III, Caravelle,  JHW
II, JHW III, JHW Strategic III, JHW Mezzanine,  Clark,  Tomick,  Bryne,  Waller,
Kitty Hawk III, Kitty Hawk IV, Eagle Creek, Finley LP, NCEF, Lutkewich, Jackman,
Eckert,   Gupton,  Price  LP  and  Benake.   Unless  otherwise  defined  herein,
capitalized terms shall have such meanings ascribed to them in the Stockholders'
Agreement.

     WHEREAS,  at  the  Company's  annual  meeting  of  stockholders  for  2001,
stockholders of the Company will,  among other things,  vote to elect members of
the  Company's  Board of Directors  (the "Board") to serve until the next annual
meeting; and

     WHEREAS,  pursuant to Section 1 of the  Stockholders'  Agreement,  the WCAS
Purchasers,  the Whitney  Purchasers,  TPC and SBCT are  entitled  to  designate
nominees for the Board; and

     WHEREAS,  such Stockholders  have designated the following  nominees to the
Board:  the WCAS  Purchasers have  designated  Thomas E. McInerney,  Lawrence B.
Sorrel and James R. Matthews;  the Whitney Purchasers have designated Michael R.
Stone;  TPC has designated  Timothy M. Donahue and Steven M. Shindler;  and SBCT
has designated Edgar L. Reynolds; and

     WHEREAS, such nominees, together with Stephen H. Clark, Calvin J. Payne and
Michael J. Price as current  directors  who will also be  nominees to the Board,
provide for a ten (10) person slate of directors for the Board; and

     WHEREAS,  Amendment No. 2 to the  Stockholders'  Agreement  amended Section
1(a)(i) of the Stockholders'  Agreement to provide, in pertinent part, that "the
authorized  number of directors of the [Board]  shall be  established  at twelve
(12) persons...."; and

     WHEREAS, pursuant to Section 18 of the Stockholders' Agreement, the Company
and the  Stockholders  desire to amend the  Stockholders'  Agreement  to further
amend  Section  1(a)(i) to allow  more  flexibility  in setting  the size of the
Board, as more particularly set forth herein.

     NOW,  THEREFORE,  in consideration of the premises and the mutual covenants
and agreements contained herein, the parties hereby agree as follows:

     1. Amendment of Section 1(a)(i).

     Section  1(a)(i) of the  Stockholders'  Agreement is hereby  amended in its
entirety and replaced with the following:

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                                      -2-

               "(i) the authorized number of directors of the board of directors
          of the  Company  (the  "Board")  to be  established  at such number of
          directors  as will  accommodate  all  persons  designated  pursuant to
          clause (ii) below,  or, at the request of the holders of a majority of
          the Common Stock then held by the WCAS Purchasers,  an increase in the
          size of the Board, up to a maximum of fifteen (15) persons;"

     2. Continuing Effect of Stockholders'  Agreement.  This Amendment shall not
constitute  an  amendment  or   modification  of  any  other  provision  of  the
Stockholders'  Agreement not expressly  referred to herein.  Except as expressly
amended or modified herein,  the provisions of the  Stockholders'  Agreement are
and shall remain in full force and effect.

     3.  Counterparts.  This  Amendment  may be  executed  by one or more of the
parties hereto on any number of separate  counterparts and all such counterparts
shall be deemed to be one and the same  instrument.  Each party hereto  confirms
that any facsimile copy of such party's  executed  counterpart of this Amendment
(or its  signature  page  thereof)  shall be deemed to be an  executed  original
thereof.

     4. Governing Law. This Amendment  shall be governed by, and interpreted and
construed  in  accordance  with,  the  internal  laws of the State of  Delaware,
without regard to principles of conflicts of law.



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         IN WITNESS WHEREOF, each of the parties hereto has executed this
agreement, as of the day and year first above written.


                 WELSH, CARSON, ANDERSON & STOWE VIII, L.P.

                 By:   WCAS VIII Associates, L.L.C.,
                       its General Partner


                 By: /s/Lawrence B. Sorrel
                     -------------------------------------------------
                       Name:Lawrence B. Sorrel
                       Title:Managing Member


                 WCAS CAPITAL PARTNERS III, L.P.

                 By:   WCAS CP III Associates, L.L.C.,
                       its General Partner


                 By: /s/Lawrence B. Sorrel
                     -------------------------------------------------
                       Name:Lawrence B. Sorrel
                       Title:Managing Member


                 WCAS INFORMATION PARTNERS, L.P.


                 By: /s/Lawrence B. Sorrel
                     -------------------------------------------------
                       Name:Lawrence B. Sorrel
                       Title:Managing Member


                 TOWER PARENT CORP.


                 By: /s/Steven Shindler
                     -------------------------------------------------
                       Name:Steven Shindler
                       Title:Chief Executive Officer, Nextel International


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                 CIBC WG ARGOSY MERCHANT FUND 2, L.L.C.


                 By: /s/Andrew R. Heyer
                     -------------------------------------------------
                       Name:Andrew R. Heyer
                       Title:Managing Member


                 CO-INVESTMENT MERCHANT FUND 3, LLC


                 By: /s/Andrew R. Heyer
                     -------------------------------------------------
                       Name:Andrew R. Heyer
                       Title:Managing Member


                 CARAVELLE INVESTMENT FUND, L.L.C.

                 By:   Caravelle Advisors, L.L.C., as its Investment Manager
                       and Attorney-in-Fact


                 By: /s/Andrew R. Heyer
                     -------------------------------------------------
                       Name:Andrew R. Heyer
                       Title:Managing Member

                 WHITNEY EQUITY PARTNERS, L.P.

                 By:   Whitney Equity Partners, LLC, its General Partner


                 By: /s/Michael R. Stone
                     -------------------------------------------------
                       Name:Michael R. Stone
                       Title:Managing Member

                 J.H. WHITNEY III, L.P.

                 By:   J.H. Whitney Equity Partners III, LLC, its General
                       Partner


                 By: /s/Michael R. Stone
                     -------------------------------------------------
                       Name:Michael R. Stone
                       Title:Managing Member
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                 WHITNEY STRATEGIC PARTNERS III, L.P.

                 By:   J.H. Whitney Equity Partners III L.L.C., its General
                       Partner


                 By: /s/Michael R. Stone
                     -------------------------------------------------
                       Name:Michael R. Stone
                       Title:Managing Member


                 WHITNEY MEZZANINE FUND, L.P.

                 By:   Whitney GP, LLC,
                       Its General Partner


                 By: /s/Michael R. Stone
                     -------------------------------------------------
                       Name:Michael R. Stone
                       Title:Managing Memeber

                 ------------------------------------
                 Stephen H. Clark


                 ------------------------------------
                 David P. Tomick


                 SBC TOWER HOLDINGS LLC

                 By:   New Southwestern Bell Mobile Systems, Inc., its
                       Managing Member


                 By: /s/Gregory L. Gibson
                     -------------------------------------------------
                       Name:Gregory L. Gibson
                       Title:Vice President