EXHIBIT 99.4
 
                         NEXTLINK COMMUNICATIONS, INC.
 
               OFFER FOR ALL OUTSTANDING 9% SENIOR NOTES DUE 2008
             IN EXCHANGE FOR UP TO $335,000,000 PRINCIPAL AMOUNT OF
                            9% SENIOR NOTES DUE 2008
 
THE EXCHANGE OFFER WILL EXPIRE AT MIDNIGHT, NEW YORK CITY TIME, ON JULY 10,
1998, UNLESS EXTENDED OR TERMINATED (THE "EXPIRATION DATE").
 
To Brokers, Dealers, Commercial Banks
  Trust Companies and Other Nominees:
 
    Enclosed for your consideration is a Prospectus dated June 10, 1998 (as the
same may be amended or supplemented form time to time, the "Prospectus") and a
form of Letter of Transmittal (the "Letter of Transmittal") relating to the
offer (the "Exchange Offer") by NEXTLINK Communications, Inc. (the "Company") to
exchange up to $335,000,000 in aggregate principal amount of its Senior Notes
due 2008 (the "New Notes") for $335,000,000 in aggregate principal amount of its
Senior Notes due 2008 (the "Old Notes").
 
    We are asking you to contact your clients for whom you hold Old Notes
registered in your name or in the name of your nominee. In addition, we ask you
to contact your clients who, to your knowledge, hold Old Notes registered in
their own name. The Company will not pay any fees or commissions to any broker,
dealer or other person in connection with the solicitation of tenders pursuant
to the Exchange Offer. You will, however, be reimbursed by the Company for
customary mailing and handling expenses incurred by you in forwarding any of the
enclosed materials to your clients. The Company will pay all transfer taxes, if
any, applicable to the tender any of the enclosed materials to your clients. The
Company will pay all transfer taxes, if any, applicable to the tender of Old
Notes to it or its order, except as otherwise provided in the Prospectus and the
Letter of Transmittal.
 
    Enclosed are copies of the following documents:
 
    1.  The Prospectus;
 
    2.  A Letter of Transmittal for your use in connection with the tender of
       Old Notes and for the information of your clients;
 
    3.  A form of letter that may be sent to your clients for whose accounts you
       hold Old Notes registered in your name or the name of your nominee; with
       space provided for obtaining the clients' instructions with regard to the
       Exchange Offer;
 
    4.  A form of Notice of Guaranteed Delivery; and
 
    5.  Guidelines for Certification of Taxpayer Identification Number on
       Substitute Form W-9.
 
    Your prompt action is requested. The Exchange Offer will expire at 5:00
p.m., New York City Time, on July 10, 1998, 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.
 
    In all cases, exchanges of Old Notes for New Notes accepted for exchange
pursuant to the Exchange Offer will be made only after timely receipt by the
Exchange Agent of (a) certificates representing such Old Notes or a confirmation
of a book-entry transfer of such Old Notes, as the case may be, (b) the Letter
of Transmittal (or a facsimile thereof) promptly completed and duly executed
with any required signature guarantees, and (c) any other documents required by
the Letter of Transmittal.
 
    Holders who wish to tender their Old Notes and (a) whose Old Notes are not
immediately available, (b) who cannot deliver their Old Notes, the Letter of
Transmittal or any other required documents to the

Exchange Agent prior to the Expiration Date or (c) who cannot complete the
procedure for book-entry transfer on a timely basis, may tender their Old Notes
by following the guaranteed delivery procedures described in the Prospectus
under "The Exchange Offer--Guaranteed Delivery Procedures."
 
    To tender Old Notes, certificates for Old Notes, a duly executed and
properly completed Letter of Transmittal or a facsimile thereof, together with
any other required documents, must be received by the Exchange Agent as provided
the Prospectus and the Letter of Transmittal.
 
    Additional copies of the enclosed material may be obtained form the Exchange
Agent, United States Trust Company, by calling (212) 852-1664.
 
    NOTHING HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU OR ANY
PERSON AS AN AGENT OF THE COMPANY OR THE EXCHANGE AGENT, OR AUTHORIZE YOU OR ANY
OTHER PERSON TO MAKE ANY STATEMENTS ON BEHALF OF EITHER OF THEM WITH RESPECT TO
THE EXCHANGE OFFER, EXCEPT FOR STATEMENTS EXPRESSLY MADE IN THE PROSPECTUS AND
THE LETTER OF TRANSMITTAL.