NEXTLINK COMMUNICATIONS, INC.
 
                                 EXCHANGE OFFER
                                 TO HOLDERS OF
              14% SENIOR EXCHANGEABLE REDEEMABLE PREFERRED SHARES
 
                         NOTICE OF GUARANTEED DELIVERY
 
    As set forth in the Prospectus dated            , 1997 (the "Prospectus") of
NEXTLINK Communications, Inc. (the "Company") under "The Exchange Offer--How to
Tender" and in the Letter of Transmittal for 14% Senior Exchangeable Redeemable
Preferred Shares (the "Letter of Transmittal"), this form or one substantially
equivalent hereto must be used to accept the Exchange Offer (as defined below)
of the Company if: (i) certificates for the above-referenced Notes (the "Old
Preferred Shares") are not immediately available; or (ii) time will not permit
all required documents to reach the Exchange Agent (as defined below) on or
prior to the Expiration Date (as defined in the Prospectus) of the Exchange
Offer. Such form may be delivered by hand or transmitted by telegram, telex,
facsimile transmission or letter to the Exchange Agent.
 
       TO: CONTINENTAL STOCK TRANSFER & TRUST COMPANY (the "Exchange Agent")
                                   2 Broadway
                            New York, New York 10004
                      Attention: Reorganization Department
                           Phone: (212) 509-4000 x535
                              Fax: (212) 509-5150
 
       DELIVERY OF THIS INSTRUMENT TO AN ADDRESS OTHER THAN AS SET FORTH
     ABOVE OR TRANSMITTAL OF THIS INSTRUMENT TO A FACSIMILE OR TELEX NUMBER
      OTHER THAN AS SET FORTH ABOVE DOES NOT CONSTITUTE A VALID DELIVERY.

Ladies and Gentlemen:
 
    The undersigned hereby tenders to the Company, upon the terms and conditions
set forth in the Prospectus and the Letter of Transmittal (which together
constitute the "Exchange Offer"), receipt of which are hereby acknowledged, the
number of Old Preferred Shares set forth below pursuant to the guaranteed
delivery procedure described in the Prospectus and the Letter of Transmittal.
 

                                   
                                                           Sign Here
 
Number of Old                         Signature(s)
Preferred Shares
Certificate Nos.                      Please Print the Following Information
(if available)                        Name(s)
Total Number
Represented by Old Preferred          Address
Shares
  Certificate(s)                      Area Code and Tel. No(s).
Account Number
Dated: , 1997


                                   GUARANTEE
 
    The undersigned, a member of a recognized signature guarantee medallion
program within the meaning of Rule 17A(d)-15 under the Securities Exchange Act
of 1934, hereby guarantees that the above-named person(s) own(s) the
above-described securities tendered hereby and that delivery to the Exchange
Agent of certificates tendered hereby, in proper form for transfer, or delivery
of such certificates pursuant to the procedure for book-entry transfer, in
either case with delivery of a properly completed and duly executed Letter of
Transmittal (or facsimile thereof) and any other required documents, is being
made within five trading days after the date of execution of a Notice of
Guaranteed Delivery of the above-named person.
 

                                             
                                                -------------------------------------------
                                                                Name of Firm
 
                                                -------------------------------------------
                                                            Authorized Signature
 
                                                -------------------------------------------
                                                       Number and Street or P.O. Box
 
                                                -------------------------------------------
                                                City             State             Zip Code
 
                                                -------------------------------------------
                                                           Area Code and Tel. No.
 
Dated: , 1997