<PAGE>   1
                        AGREEMENT AND NOTICE OF EXCHANGE

        This Agreement (this "Agreement") is made as of September 13, 2000, by
and between Cook Inlet GSM, Inc., a Delaware corporation ("Cook Inlet") and
VoiceStream Wireless Corporation ("VoiceStream"), a Delaware corporation.
Capitalized terms not defined shall have the meaning ascribed to them in the
Exchange Rights Agreements (as defined below).

        WHEREAS, Cook Inlet and VoiceStream have entered into three (3) separate
Exchange Rights Agreements dated as of May 3, 1999; February 25, 2000; and
February 25, 2000, (together, the "Exchange Rights Agreements") whereby
VoiceStream granted, and Cook Inlet accepted, the right to exchange Cook Inlet's
entire ownership rights and interests in Cook Inlet GSM Control LLC, Cook
Inlet/VS GSM II PCS, LLC, and Cook Inlet/VS GSM III PCS, LLC, respectively, for
shares of VoiceStream Common Stock, subject to the terms and conditions set
forth therein.

        WHEREAS, the Exchange Rights Agreements provide that, in the event that
FCC Rules are amended such that neither License forfeiture nor violation of the
C and F block eligibility requirements (as defined by the FCC Rules) would occur
as a result of the Exchange occurring sooner than five (5) years after the date
of the initial License grant, the Exchange Date shall be advanced;

        WHEREAS, the parties believe that the FCC Rules were so amended, and
VoiceStream has provided a legal opinion from outside counsel acceptable to Cook
Inlet so stating, as required by the Exchange Rights Agreements; and

        WHEREAS, Cook Inlet and VoiceStream desire that Cook Inlet effect an
Exchange and exercise its Exchange Rights pursuant to all of the Exchange Rights
Agreements in one transaction qualifying as a reorganization under the
provisions of Section 368 of the Internal Revenue Code of 1986, as amended (the
"Code").

        NOW THEREFORE, pursuant to the terms and conditions set forth herein and
in the Exchange Rights Agreements, the parties, intending to be bound legally,
agree as follows:

        1. The "Exchange Date" under the Exchange Rights Agreements shall be
September 1, 2000.

        2. By this Agreement, Cook Inlet has irrevocably elected to exchange all
of its Control Group Interest or Company Interest, as the case may be, pursuant
to the applicable Exchange Rights Agreement, and this Agreement shall serve as
an effective Exchange Notice pursuant to the Exchange Rights Agreements. Cook
Inlet shall receive the following number of shares of VoiceStream Common Stock
(subject to adjustment in accordance with the terms of the Exchange Rights
Agreements) in exchange for all of its Control Group Interest or Company
Interest, as the case may be, pursuant to the applicable Exchange Rights
Agreement:

<TABLE>
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    INTEREST TO BE EXCHANGED        APPLICABLE EXCHANGE RIGHTS         NUMBER OF SHARES OF
        (APPLICABLE LLC)                    AGREEMENT                VOICESTREAM COMMON STOCK
-------------------------------------------------------------------------------------------------
<S>                               <C>                                       <C>
Control Group Interest (Cook      Exchange Rights Agreement                 4,009,803
Inlet GSM Control LLC)            dated as of May 3, 1999

-------------------------------------------------------------------------------------------------
Member Interest (Cook Inlet/VS    Exchange Rights Agreement                 3,000,000
GSM II PCS, LLC)                  (CI-VS II) dated as of
                                  February 25, 2000)

-------------------------------------------------------------------------------------------------
Member Interest (Cook Inlet/VS    Exchange Rights Agreement                   750,000
GSM III PCS, LLC)                 (CI-VS III) dated as of
                                  February 25, 2000
-------------------------------------------------------------------------------------------------
</TABLE>




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<PAGE>   2

        3. In order to facilitate the Exchanges, the parties shall as soon as
reasonably practicable (i) file applications with the Federal Communications
Commission requesting consent to the transfer of control of the various licenses
controlled by Cook Inlet, (ii) file such Notification and Report Forms as may be
required under the Hart-Scott-Rodino Act, and (iii) enter into an Agreement and
Plan of Reorganization which shall provide for (a) the transfer of the assets of
Cook Inlet, which consist solely of the Control Group Interest and the Company
Interests, in exchange for the shares of VoiceStream Common Stock deliverable to
Cook Inlet pursuant to the Exchange Rights Agreements in a transaction
qualifying as a reorganization under the provisions of Section 368 of the Code,
and (b) the assumption of only those liabilities arising out of the acquired
assets.

        4. This Agreement does not, and shall not be deemed to, supersede,
amend, modify, waive or replace the Exchange Rights Agreements or any of the
provisions thereof.







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<PAGE>   3

        IN WITNESS WHEREOF, the parties hereto have duly executed and delivered
this Agreement on the day and year first above written.



VOICESTREAM WIRELESS CORPORATION


By:   /s/ David Miller
      -------------------------------
Its:  Vice President of Legal Affairs
      -------------------------------


COOK INLET GSM, INC.


By:   /s/ Craig Floerchinger
      -------------------------------
Its:  Vice President
      -------------------------------




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