NEXTLINK COMMUNICATIONS, INC.

              OFFER FOR ALL OUTSTANDING 10 1/2% SENIOR NOTES DUE 2009
           AND ALL OUTSTANDING 12 1/8% SENIOR DISCOUNT NOTES DUE 2009
             IN EXCHANGE FOR UP TO $400,000,000 PRINCIPAL AMOUNT OF
        10 1/2% SENIOR NOTES DUE 2009 AND $455,000,000 PRINCIPAL AMOUNT
            OF 12 1/8% SENIOR DISCOUNT NOTES DUE 2009, RESPECTIVELY

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THE EXCHANGE OFFER WILL EXPIRE AT 5:00 P.M., NEW YORK CITY TIME, ON MAY 3, 1999,
   UNLESS EXTENDED OR TERMINATED (THE "EXPIRATION DATE").
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To Our Clients:

    Enclosed for your consideration is a Prospectus dated       , 2000 (as the
same may be amended or supplemented from time to time, the "Prospectus") and two
forms of Letter of Transmittal (each a "Letter of Transmittal") relating to the
offer (the "Exchange Offer") by NEXTLINK Communications, Inc. (the "Company") to
exchange up to $400,000,000 in aggregate principal amount of its Senior Notes
due 2009 and $455,000,000 principal amount of Senior Discount Notes Due 2009
(collectively, the "New Notes") for $400,000,000 in aggregate principal amount
of its Senior Notes due 2009 and $455,000,000 principal amount of Senior
Discount Notes Due 2009 (collectively, the "Old Notes"), respectively.

    The material is being forwarded to you as the beneficial owner of Old Notes
held by us for your account or benefit but not registered in your name. A tender
of the Old Notes pursuant to the Exchange Offer may be made only by us as the
registered holder of the Old Notes, and pursuant to your instructions.
Therefore, the Company urges beneficial owners of Old Notes registered in the
name of a broker, dealer, commercial bank, trust company or other nominee to
contact such holder promptly if they wish to tender Old Notes in the Exchange
Offer.

    Accordingly, we request instructions as to whether you wish us to tender any
or all Old Notes held by us for your account or benefit, pursuant to the terms
and conditions set forth in the Prospectus and the appropriate Letter of
Transmittal. We urge you to read carefully the Prospectus and such Letter of
Transmittal before instructing us to tender your Old Notes pursuant to the
Exchange Offer.

    Your instructions to us should be forwarded as promptly as practicable in
order to permit us to tender Old Notes on your behalf in accordance with the
provisions of the Exchange Offer. The Exchange Offer will expire at 5:00 p.m.,
New York City Time, on             , 2000 unless extended (the "Expiration
Date"). Old Notes tendered pursuant to the Exchange Offer may be withdrawn,
subject to the procedures described in the Prospectus, at any time prior to the
Expiration Date.

    If you wish to have us tender any or all of your Old Notes held by us for
your account or benefit, please so instruct us by completing, executing and
returning to us the instruction form that appears below. The accompanying Letter
of Transmittal is furnished to you for informational purposes only and may not
be used by you to tender Old Notes held by us and registered in our name for
your account or benefit.

                INSTRUCTIONS WITH RESPECT TO THE EXCHANGE OFFER

    The undersigned acknowledge(s) receipt of your letter and the enclosed
material referred to therein relating to the Exchange Offer made by NEXTLINK
Communications, Inc. with respect to their Old Notes.

    This will instruct you to tender the Old Notes held by you for the account
of the undersigned, upon and subject to the terms and conditions set forth in
the Prospectus and the related Letter of Transmittal.

    Please tender the Old Notes held by you for my account as indicated below:

                                        AGGREGATE PRINCIPAL AMOUNT
                                        OF OLD NOTES

                                        ----------------------------------------

/ / Please do not tender any Old Notes
  held by you for my account

Dated: ____________, 2000

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                                                       Signature(s)

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                                                Please Print Name(s) here

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                                                       Address(es)

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                                           Area Code(s) and Telephone Number(s)

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                                          Tax Identification or Social Security
                                          No(s)

None of the Old Notes held by us for your account will be tendered unless we
receive written instructions from you to do so. Unless a specific instruction is
given in the space provided, your signature(s) hereon shall constitute an
instruction to us to tender all the Old Notes held by us for your account.

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