NEXTLINK COMMUNICATIONS INC / DE
424B3, 1999-04-01
TELEPHONE COMMUNICATIONS (NO RADIOTELEPHONE)
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<PAGE>
                                             Filed Pursuant to Rule 424(b)(3)
                                             Registration No. 333-71749
 
                                     [LOGO]
 
                         NEXTLINK COMMUNICATIONS, INC.
 
                               EXCHANGE OFFER FOR
                         10 3/4% SENIOR NOTES DUE 2008
 
    This is an offer to exchange the outstanding, unregistered NEXTLINK 10 3/4%
Senior Notes you now hold for new, substantially identical 10 3/4% Senior Notes
that will be free of the transfer restrictions that apply to the old notes. This
offer will expire at 5:00 p.m., New York City time, on May 3, 1999, unless we
extend it. You must tender your old, unregistered notes by the deadline to
obtain new, registered notes and the liquidity benefits they offer.
 
    We agreed with the initial purchasers of the old notes to make this offer
and register the issuance of the new notes following the closing. This offer
applies to any and all old notes tendered by the deadline.
 
    The new notes will not trade on any established exchange. The new notes have
the same financial terms and covenants as the old notes, and are subject to the
same business and financial risks.
 
    A DESCRIPTION OF THOSE RISKS BEGINS ON PAGE 11.
 
    NEITHER THE SEC NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR
DISAPPROVED OF THESE SECURITIES OR PASSED UPON THE ADEQUACY OR ACCURACY OF THIS
PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.
 
                                 April 1, 1999
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                               TABLE OF CONTENTS
 
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                                                                                                                PAGE
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Nextlink....................................................................................................          1
Risk Factors................................................................................................         11
Where You Can Find More Information.........................................................................         18
Delivery Of Prospectus......................................................................................         18
Use Of Proceeds.............................................................................................         18
Capitalization..............................................................................................         19
Business....................................................................................................         20
Regulation..................................................................................................         26
The Exchange Offer..........................................................................................         28
Description Of The Notes....................................................................................         41
Book-Entry; Delivery and Form...............................................................................         85
Description Of Material Indebtedness........................................................................         87
Material United States Federal Income Tax Consequences......................................................         93
Plan Of Distribution........................................................................................         97
Incorporation Of Material Documents By Reference............................................................         99
Legal Matters...............................................................................................         99
Experts.....................................................................................................         99
</TABLE>
 
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                                    NEXTLINK
 
    We provide high-quality local and long distance telecommunications and data
services to small and medium-sized businesses in 38 U.S. cities. We offer our
customers these services at competitive prices individually or as an integrated
package of services. We deliver these services over networks that consist of
communications cables containing multiple glass fiber strands, known as fiber
optic cables. These cables connect our customers' telephone and data lines to
our advanced, electronic switching equipment, or switches, which route each call
from the customer's premises to the ultimate call destination. Each of our
networks can carry high volumes of voice, data, video and Internet traffic.
Whenever practicable, we build and own these networks ourselves.
 
    We currently operate 23 fiber optic networks in 14 states, serving large and
medium-sized cities, as well as clusters of smaller locales. Based on our recent
successes in operating and expanding our existing networks, as well as
opportunities arising in cities we do not currently serve, we intend to expand
into a number of new locations over the next several years.
 
    In each city we serve, our principal competitor is the dominant local
telephone company, which Congress and our industry refer to as the incumbent
local exchange carrier. Until recently, each incumbent carrier held a virtual
monopoly on providing local telephone service. Our goal is for businesses
located in the cities we serve to choose to have their telephone and data lines
connected to our network, rather than that of the incumbent. In constructing
each network, we create a ring of fiber optic cables around the central business
district of each location we serve. This design allows for a high percentage of
the commercial buildings within these locations to be connected directly to our
networks. A number of our customers, however, are not directly connected to our
networks. For these customers, we lease telephone lines from the incumbent
carrier to cover the relatively short distance between the customer and our
network. We plan to increase the number of businesses that we can connect
directly to our networks by using fixed wireless radio spectrum that we control
or have contracts to acquire in the majority of the top 30 U.S. cities.
 
    We are developing plans to link our local fiber optic networks to one
another through the use of a national fiber optic network currently being
constructed by Level 3 Communications. We manage and own 50% of a joint venture
that owns exclusive interests in the Level 3 network. This network is designed
to traverse more than 16,000 miles, connecting 50 cities in the United States
and Canada. With this system of local networks linked together by long-haul
fiber optic cable, we should be able to offer our customers complete, end-to-end
voice and data communications services over facilities we control.
 
    We also are developing plans to deploy data switching and transmission
equipment in 2000 that will enable us to provide a full range of innovative data
 
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services. The Level 3 network is also designed to support the types of equipment
necessary to provided these data services, in addition to voice services.
 
    Our founder and principal shareholder, Craig McCaw, also founded McCaw
Cellular (later acquired by AT&T) and has substantial interests in other
telecommunications businesses.
 
BUSINESS STRATEGY
 
    Our goal is to become a leading provider of complete, end-to-end voice and
data communications services and to maximize penetration of our targeted
customer base of small and medium-sized businesses. The key components of our
strategy to achieve this goal are:
 
    - Building high-capacity local networks with cables holding large bundles of
      fiber optic strands in a majority of the nation's top 30 cities and
      providing service in cities with a total of 27 million business lines by
      the end of 2000.
 
    - Increasing direct customer connections to our networks using fixed
      wireless radio spectrum.
 
    - Linking our local networks to one another using our interest in a national
      fiber optic network now under construction.
 
    - Deploying advanced switching equipment on our fiber optic network,
      including technology known as Asynchronous Transfer Mode, or ATM, designed
      for high speed voice and video communications, and technologies known as
      frame relay and Internet Protocol, or IP, designed for high-speed
      facsimile, e-mail and other data communications.
 
    - Deploying advanced transmission equipment, known as digital subscriber
      line, or DSL, designed to increase the speed of digital transmissions over
      copper telephone wires.
 
    - Attracting and retaining experienced management and maintaining a
      decentralized, local management focus at each operating subsidiary.
 
    - Focusing sales efforts on businesses and professional groups with fewer
      than 50 telephone lines, and assigning a single customer care
      representative to each customer.
 
    - Continuously improving the complex process of the changing over a new
      customer from the incumbent carrier to NEXTLINK service.
 
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                               THE EXCHANGE OFFER
 
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The Exchange Offer............  We are offering to exchange $1,000 principal amount at
                                maturity of NEXTLINK's 10 3/4% Senior Notes due 2008 which
                                have been registered under the Securities Act for each
                                $1,000 principal amount at maturity of NEXTLINK's
                                outstanding 10 3/4% Senior Notes due 2008 which were issued
                                in November 1998 in a private offering. In order to be
                                exchanged, an old note must be properly tendered and
                                accepted. We will exchange all notes validly tendered and
                                not validly withdrawn. As of this date there is $500.0
                                million aggregate principal amount at maturity of old notes
                                outstanding.
 
Expiration and Exchange
 Dates........................  This offer will expire at 5:00 p.m., New York City time, on
                                May 3, 1999, unless we extend it, and we will consummate
                                the exchange on the next business day.
 
Registration Rights
 Agreement....................  You have the right to exchange the old notes that you now
                                hold for new notes with substantially identical terms. This
                                exchange offer is intended to satisfy these rights. After
                                the exchange offer is complete, you will no longer be
                                entitled to any exchange or registration rights with
                                respect to your notes.
 
Conditions....................  This offer is conditioned only upon compliance with the
                                securities laws. The offer applies to any and all old notes
                                tendered by the deadline.
 
Withdrawal Rights.............  You may withdraw your tender of old notes at any time
                                before the offer expires.
 
Federal Income Tax
 Consequences.................  The exchange will not be a taxable event for United States
                                federal income tax purposes. You will not recognize any
                                taxable gain or loss or any interest income as a result of
                                such exchange.
 
Resale Without Further
 Registration.................  We believe that the new notes may be offered for resale,
                                resold and otherwise transferred by you without compliance
                                with the registration and prospectus delivery provisions of
                                the Securities Act so long as the following statements are
                                true:
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<S>                             <C>
                                - you acquire the new notes issued in the exchange offer in
                                  the ordinary course of your business;
 
                                - you are not an "affiliate," as defined under Rule 405 of
                                  the Securities Act, of ours;
 
                                - you are not participating, and do not intend to
                                  participate, and have no arrangement or understanding
                                  with any person to participate, in the distribution of
                                  the new notes issued to you in the exchange offer.
 
                                By tendering your notes as described below, you will be
                                making representations to this effect.
 
Transfer Restrictions on New
 Notes........................  You may incur liability under the Securities Act if:
 
                                (1)any of the representations listed above are not true;
                                   and
 
                                (2)you transfer any new note issued to you in the exchange
                                   offer without:
 
                                - delivering a prospectus meeting the requirements of the
                                  Securities Act; or
 
                                - an exemption from the Securities Act's requirements to
                                  register your new notes.
 
                                We do not assume or indemnify you against such liability.
                                Each broker-dealer that is issued new notes for its own
                                account in exchange for old notes that were acquired as a
                                result of market-making or other trading activities, must
                                acknowledge that it will deliver a prospectus meeting the
                                requirements of the Securities Act in connection with any
                                resale of the new notes. A broker-dealer may use this
                                prospectus for an offer to resell, a resale or other
                                retransfer of the new notes issued to it in the exchange
                                offer.
 
Procedures for Tendering Old
 Notes........................  Each holder of old notes who wishes to accept the exchange
                                offer must:
 
                                - complete, sign and date the accompanying letter of
                                  transmittal, or a facsimile thereof; or
 
                                - arrange for the The Depository Trust Company to transmit
                                  certain required information to the
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<S>                             <C>
                                  exchange agent in connection with a book-entry transfer.
 
                                You must mail or otherwise deliver such documentation and
                                your old notes to the United States Trust Company of New
                                York, as exchange agent, at the address set forth under
                                "The Exchange Offer--Exchange Agent."
 
Failure to Exchange will
 affect you adversely.........  If you are eligible to participate in the exchange offer
                                and you do not tender your old notes, you will not have any
                                further registration or exchange rights and your old notes
                                will continue to be subject to some restrictions on
                                transfer. Accordingly, the liquidity of the old notes could
                                be adversely affected.
 
Special Procedures for
 Beneficial Owners............  If you beneficially own old notes registered in the name of
                                a broker, dealer, commercial bank, trust company or other
                                nominee and you wish to tender your old notes in the
                                exchange offer, you should contact such registered holder
                                promptly and instruct it to tender on your behalf. If you
                                wish to tender on your own behalf, you must, before
                                completing and executing the letter of transmittal for the
                                exchange offer and delivering your old notes, either
                                arrange to have your old notes registered in your name or
                                obtain a properly completed bond power from the registered
                                holder. The transfer of registered ownership may take
                                considerable time.
 
Guaranteed Delivery
 Procedures...................  You may comply with the procedures described in this
                                prospectus under the heading "The Exchange Offer--
                                Guaranteed Delivery Procedures" if you wish to tender your
                                old notes and:
 
                                - time will not permit your required documents to reach the
                                  exchange agent by the expiration date of the exchange
                                  offer,
 
                                - you cannot complete the procedure for book-entry transfer
                                  on time, or
 
                                - your old notes are not immediately available.
</TABLE>
 
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<PAGE>
                                 THE NEW NOTES
 
    The new notes have the same financial terms and covenants as the old notes,
which are as follows:
 
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Issuer........................  NEXTLINK Communications, Inc.
 
Maturity......................  November 15, 2008.
 
Interest......................  Interest accrues from November 12, 1998 at the rate of
                                10 3/4% per year, payable semi-annually in arrears on each
                                May 15 and November 15, beginning on May 15, 1999.
 
Ranking.......................  The new notes are unsecured indebtedness of NEXTLINK.
 
Optional Redemption...........  On or after November 15, 2003, we will have the right to
                                redeem any or all of the new notes at their principal
                                amount plus accrued interest and a premium initially equal
                                to 5.375% and declining after that date.
 
                                In addition, before November 15, 2001, we have the right to
                                use the net cash proceeds of qualifying offerings of stock
                                to redeem up to 33 1/3% of the new notes originally
                                outstanding at their principal amount plus accrued interest
                                and a premium of 12.75%. For more information, see
                                "Description of the Notes--Optional Redemption".
 
Change of Control.............  If an event treated as a change of control of NEXTLINK
                                occurs, NEXTLINK must make an offer to purchase any and all
                                of the new notes then outstanding from you at a purchase
                                price equal to 101% of their aggregate principal amount,
                                plus accrued and unpaid interest, if any, to the date of
                                purchase. For a summary of what constitutes change of
                                control please see "Description of the
                                Notes--Covenants--Change of Control".
 
Covenants.....................  The indenture under which the old notes have been and the
                                new notes are being issued contains covenants for your
                                benefit which, among other things and subject to important
                                exceptions, restrict our ability and the ability of our
                                subsidiaries to:
 
                                - incur indebtedness;
 
                                - make the payments required by the indenture;
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                                - issue capital stock of certain of our subsidiaries;
 
                                - repurchase our stock or subordinated indebtedness;
 
                                - enter into transactions with stockholders and affiliates;
 
                                - create liens;
 
                                - pay dividends or make other distributions;
 
                                - engage in sale-leaseback transactions; and
 
                                - consolidate, merge or sell all or substantially all of
                                  our assets or the assets of our subsidiaries.
 
                                The indenture allows modification and amendment of these
                                and other covenants by a vote of holders of a majority in
                                aggregate principal amount of the notes, subject to
                                exceptions described in the indenture. Also, holders of a
                                majority in aggregate principal amount of the notes may
                                waive our compliance with certain other restrictive
                                covenants in the indenture.
</TABLE>
 
    For additional information regarding the notes, see "Description of the
Notes" and "Material United States Federal Income Tax Consequences."
 
                                  RISK FACTORS
 
    See "Risk Factors" immediately following this summary for a discussion of
risks relating to the new notes, all of which apply to the old notes as well.
 
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<PAGE>
          SUMMARY HISTORICAL CONSOLIDATED FINANCIAL AND OPERATING DATA
                             (DOLLARS IN THOUSANDS)
    We have summarized below our historical consolidated financial data as of
and for the years ended December 31, 1996, 1997 and 1998. This information is
derived from and qualified by reference to our audited Consolidated Financial
Statements included in our 1998 Form 10-K, which is incorporated in this
prospectus by reference. All of the data should be read in conjunction with and
are qualified by reference to "Management's Discussion and Analysis of Financial
Condition and Results of Operations" included in our 1998 Form 10-K.
 
<TABLE>
<CAPTION>
                                                                                         YEAR ENDED
                                                                                        DECEMBER 31,
                                                                          ----------------------------------------
                                                                              1996          1997          1998
                                                                          ------------  ------------  ------------
<S>                                                                       <C>           <C>           <C>
CONSOLIDATED STATEMENT OF OPERATIONS DATA:
Revenue.................................................................  $     25,686  $     57,579  $    139,667
Costs and expenses:
  Operating.............................................................        25,094        54,031       123,675
  Selling, general and administrative...................................        31,353        75,732       156,929
  Deferred compensation.................................................         9,914         3,247         4,993
  Depreciation and amortization.........................................        10,340        27,190        60,254
                                                                          ------------  ------------  ------------
Loss from operations....................................................       (51,015)     (102,621)     (206,184)
Interest expense, net...................................................       (20,086)      (26,383)      (72,156)
                                                                          ------------  ------------  ------------
Net loss................................................................  $    (71,101) $   (129,004) $   (278,340)
                                                                          ------------  ------------  ------------
                                                                          ------------  ------------  ------------
OTHER DATA:
Ratio of earnings to fixed charges(1)...................................            --            --            --
EBITDA(2)...............................................................  $    (30,761) $    (72,184) $   (140,937)
Capital expenditures, including acquisitions of businesses (net of cash
  acquired) and investments in affiliates (3)...........................        85,872       232,069       416,445
</TABLE>
 
<TABLE>
<CAPTION>
                                                                                     AS OF DECEMBER 31,
                                                                           --------------------------------------
                                                                              1996         1997          1998
                                                                           ----------  ------------  ------------
<S>                                                                        <C>         <C>           <C>
CONSOLIDATED BALANCE SHEET DATA:
Cash, cash equivalents and marketable securities.........................  $  124,520  $    742,357  $  1,478,062
Pledged securities(4)....................................................     101,438        62,610        21,500
Working capital..........................................................     137,227       744,510     1,408,501
Property and equipment, net..............................................      97,784       253,653       594,408
Total assets.............................................................     390,683     1,219,978     2,483,106
Long-term debt...........................................................     350,000       750,000     2,013,192
Redeemable preferred stock, net of issuance costs........................          --       313,319       556,168
Equity units subject to redemption.......................................       4,950            --            --
Class B common stock subject to redemption...............................          --         4,950            --
Total shareholders' equity (deficit).....................................     (18,654)       71,285      (246,463)
</TABLE>
 
- ------------------------
(1) For the years ended December 31, 1996, 1997 and 1998, earnings were
    insufficient to cover fixed charges during the periods presented by the net
    loss amounts of $71,101, $129,004, and $278,340, respectively.
(2) EBITDA consists of net loss before net interest expense, depreciation,
    amortization and deferred compensation expense. EBITDA is commonly used to
    analyze companies on the basis of operating performance, leverage and
    liquidity. While EBITDA should not be construed as a substitute for
    operating income or a better measure of liquidity than cash flow from
    operating activities, which
 
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    are determined in accordance with generally accepted accounting principles,
    it is included herein to provide additional information with respect to the
    anticipated ability of NEXTLINK to meet future debt service, capital
    expenditures and working capital requirements.
(3) Total capital expenditures, acquisitions, and investments in affiliates were
    funded as follows:
 
<TABLE>
<CAPTION>
                                                                                        YEAR ENDED
                                                                                       DECEMBER 31,
                                                                             ---------------------------------
                                                                               1996        1997        1998
                                                                             ---------  ----------  ----------
<S>                                                                          <C>        <C>         <C>
Cash expended..............................................................  $  72,042  $  210,545  $  416,445
Debt issued and assumed....................................................      8,228       5,000          --
Equity issued..............................................................      5,602      16,524          --
                                                                             ---------  ----------  ----------
Total......................................................................  $  85,872  $  232,069  $  416,445
                                                                             ---------  ----------  ----------
                                                                             ---------  ----------  ----------
</TABLE>
 
(4) Pledged U.S. Treasury securities, which represent funds sufficient to
    provide for payment in full of interest through April 15, 1999 on our
    12 1/2% Senior Notes.
 
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<PAGE>
    The table below contains operating data, including statistics of our Las
Vegas network which we manage and in which we have a 40% membership interest. In
this table, a "route mile" measures the expansiveness of our network, and is
equal to the number of physical miles along which we have installed or leased
fiber optic cable. A "fiber strand" is an advanced telephone line which can
carry a large volume of telephone calls and data transmissions. The number of
"fiber miles" that we have installed is equal to our estimate of the number of
fiber strands that we have installed along our network, multiplied by the number
of route miles covered by our network. It is a measure of our carrying capacity
of large volumes of telephone calls and data transmissions.
    "On-net buildings connected" means buildings physically connected to our
network, excluding those buildings which are connected to our network by
facilities leased from the incumbent telephone company. As of December 31, 1998,
we had 13,443 buildings physically connected to our network, including those
buildings connected to our network by facilities leased from the incumbent
telephone company.
    "Switches" are electronic devices that route telephone calls and data
transmissions to their final destination. All switch counts include two long
distance switches acquired in 1996 as well as the switch installed in NEXTLAB,
our telecommunications and data testing facility.
    An "access line" is a telephone connection between a customer purchasing
local telephone services and our facilities. This definition of access lines is
adjusted to reflect the fact that some high performance connections, known as
primary rate interface, can carry comparatively larger volumes of voice and data
communications. Lines over which primary rate interface service is provided are
counted as 23 access lines. The number of "access lines installed" represents
the number of access lines for which NEXTLINK is billing services. This number
includes access lines that are provisioned through the resale of services. We
serviced 2,995 resold access lines as of December 31, 1998.
 
<TABLE>
<CAPTION>
                                                     AS OF         AS OF        AS OF         AS OF          AS OF
                                                 DECEMBER 31,    MARCH 31,    JUNE 30,    SEPTEMBER 30,  DECEMBER 31,
                                                     1997          1998         1998          1998           1998
                                                 -------------  -----------  -----------  -------------  -------------
<S>                                              <C>            <C>          <C>          <C>            <C>
OPERATING DATA:
Route miles....................................        1,897         2,036        2,099         2,150          2,477
Fiber miles....................................      133,224       141,788      152,225       158,987        195,531
On-net buildings connected.....................          513           571          658           736            801
Switches installed.............................           13            14           17            18             21
Access lines installed.........................       50,131        72,834      102,887       134,107        174,182
Employees......................................        1,327         1,499        1,765         2,065          2,299
</TABLE>
 
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                                  RISK FACTORS
 
    The new notes, like the old notes, entail the following risks:
 
WE HAVE SUBSTANTIAL EXISTING DEBT AND WILL INCUR SUBSTANTIAL ADDITIONAL DEBT, SO
  WE MAY BE UNABLE TO PAY INTEREST OR PRINCIPAL ON THE NOTES THAT YOU HOLD
 
    As of December 31, 1998, NEXTLINK had outstanding five issues of senior
notes totaling $2,013.2 million in principal amount and approximately $91.9
million in miscellaneous debt obligations of its subsidiaries. Because we have
these substantial obligations, we may be unable to pay interest or principal on
the notes that you hold. Our indentures permit us to incur substantial
additional debt, and we fully expect to borrow substantial additional funds
during the next few years. These borrowings may be secured by our assets or the
assets of our subsidiaries. This additional debt may make it more difficult for
us to repay you. For more information, see "Description of the Notes" and
"Capitalization."
 
WE DO NOT CURRENTLY GENERATE CASH FLOW FROM WHICH TO MAKE PAYMENTS ON THE NOTES
  THAT YOU HOLD
 
    For the year ended December 31, 1998, we had a net loss of $278.3 million
and negative cash flow from operations of $174.5 million. Consequently, we do
not currently generate cash flows from which we can make payments on the notes
that you hold.
 
    Our plan to develop our businesses and expand our networks, which has
required and will continue require substantial capital expenditures, contributes
to our negative cash flow. We will continue to have negative cash flow and
operating losses until we begin to realize adequate revenues. We cannot assure
you that we will ever establish an adequate revenue base to produce an operating
profit or generate adequate cash flow to provide future capital expenditures and
repayment of debt.
 
SIGNIFICANT CAPITAL EXPENDITURES WILL DIVERT FUNDS WHICH COULD BE USED TO MAKE
  PAYMENTS ON THE NOTES THAT YOU HOLD
 
    We expect to make significant capital expenditures in the future. These
expenditures will divert funds which could be used to make payments on the notes
that you hold. In addition to the expenditures required to implement our
strategy discussed under "Business," additional expenditures are likely to
include the potential acquisition of other telecommunications companies and the
continued development and implementation of a comprehensive information
technology platform.
 
IF WE ARE NOT SUCCESSFUL IN RAISING ADDITIONAL CAPITAL, WE WILL NOT BE ABLE TO
  BUILD AND MAINTAIN OUR NETWORKS
 
    Because our anticipated future capital requirements will exceed the $1,478.1
million in cash and marketable securities we had on hand as of December 31,
1998, we will be required to raise additional capital. If we fail to raise
sufficient capital, we
 
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may be required to delay or abandon some of our planned future expansion or
expenditures, which could have a material adverse effect on our growth and our
ability to compete in the telecommunications services industry, and could even
result in a payment default on our existing debt.
 
BECAUSE YOUR NOTES ARE STRUCTURALLY SUBORDINATED TO THE OBLIGATIONS OF OUR
  SUBSIDIARIES, YOU MAY NOT BE FULLY REPAID IF WE BECOME INSOLVENT
 
    Because our cash flows from operations arise at the subsidiary level, all of
our senior notes are structurally subordinated to the debts of our subsidiaries.
Creditors of any NEXTLINK subsidiary, including trade creditors, have and will
have claims that are senior to the senior notes with respect to the assets of
that subsidiary. In addition, some of our subsidiaries are subject to capital
and other lease obligations.
 
OUR SUBSIDIARIES MUST MAKE PAYMENTS TO US IN ORDER FOR US TO MAKE PAYMENTS ON
  THE NOTES THAT YOU HOLD
 
    We depend upon cash payments from our subsidiaries to meet our fixed-charge
payment obligations, including our obligation to pay you as a holder of notes.
We cannot assure you that our subsidiaries will have sufficient cash to make any
payments to us, and their cash flows operations are currently negative. The
indentures generally permit us to invest proceeds from the sale of our debt
securities in subsidiaries and joint ventures that we manage.
 
BECAUSE THE NOTES THAT YOU HOLD ARE UNSECURED, YOU MAY NOT BE FULLY REPAID IF WE
  BECOME INSOLVENT
 
    The new notes will not be secured by any of the assets of NEXTLINK or its
subsidiaries. Therefore, you may not be fully repaid if we become insolvent.
Moreover, the indentures relating to the senior notes permit us to incur secured
debt. If we were to incur secured debt and we become insolvent, the holders of
the secured debt would receive payments from the assets used as security before
you receive payments.
 
IF WE CANNOT QUICKLY AND EFFICIENTLY INSTALL OUR HARDWARE, WE WILL BE UNABLE TO
  GENERATE REVENUE
 
    Each of our networks consists of many different pieces of hardware,
including switches, fiber optic cables, electronics, and wireless transmitters
and receivers which are difficult to install. If we cannot install this hardware
quickly, the time in which customers can be connected to our network and we can
begin to generate revenue from our network will be delayed. You should be aware
that the construction of the INTERNEXT national fiber optic network is not under
our control, but is under the control of Level 3 Communications. We cannot
assure you that the Level 3 network will be completed, that it will be placed in
service within the expected time frame or that it will contain the contemplated
number of fibers and conduits throughout the
 
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<PAGE>
entire network. Failure of Level 3 to complete its network would delay
implementation of our strategy of linking our local networks to one another.
 
WE MAY NOT BE ABLE TO CONNECT OUR NETWORK TO THE INCUMBENT CARRIER'S NETWORK ON
  FAVORABLE TERMS
 
    We require interconnection agreements with the incumbent carrier to connect
calls between our on-net customers and non-customers. We cannot assure you that
we will be able to negotiate or renegotiate interconnection agreements in all of
our markets on favorable terms.
 
THE REQUIREMENT THAT WE OBTAIN PERMITS AND RIGHTS OF WAY INCREASES OUR COST OF
  DOING BUSINESS
 
    In order for us to acquire and develop our fiber networks, we must obtain
local franchises and other permits, as well as rights-of-way and fiber capacity
from entities such as incumbent carriers and other utilities, railroads, long
distance companies, state highway authorities, local governments and transit
authorities. You should be aware that the process of obtaining these permits and
rights of way increases our cost of doing business.
 
    We cannot assure you that we will be able to maintain our existing
franchises, permits and rights-of-way that we need to implement our business.
Nor can we assure you that we will be able to obtain and maintain the other
franchises, permits and rights that we require. A sustained and material failure
to obtain or maintain these rights could materially adversely affect our
business in the affected metropolitan area.
 
IN LOCAL MARKETS, WE COMPETE AGAINST THE INCUMBENT CARRIER, WHICH HAS A VESTED
  INTEREST IN MAKING IT DIFFICULT TO FOR US TO CONNECT CUSTOMERS TO OUR NETWORK
 
    In each of the local markets served by our networks, we compete principally
with the incumbent carrier in that market.
 
    The incumbent carriers are already established providers of local telephone
services to all or virtually all telephone subscribers within their respective
service areas. The physical connections from their premises to those of their
customers are expensive and difficult to duplicate. In addition, they have
long-standing relationships with regulatory authorities at the federal and state
levels.
 
    It is expensive and difficult for us to switch a new customer to our network
because:
 
    - a potential customer faces switching costs if they decide to become our
      customers, and
 
    - we require cooperation from the incumbent carrier.
 
    We cannot assure you that we will be able to overcome these advantages and
compete successfully with the incumbent carriers.
 
                                       13
<PAGE>
WE MAY FACE COMPETITION IN LOCAL MARKETS FROM NEW ENTRANTS, PUTTING DOWNWARD
  PRESSURE ON PRICES
 
    We also face competition from potential market entrants, including long
distance carriers seeking to enter, reenter or expand entry into the local
exchange marketplace such as AT&T, MCI WorldCom and Sprint. This places downward
pressure on prices for local telephone service and makes it more difficult for
us to achieve positive operating cash flow. In addition, we expect competition
from other companies like ourselves, cable television companies, electric
utilities, microwave carriers, wireless telephone system operators and private
networks built by large end-users, as well as other new entrants such as Quest
Communications and Level 3. We cannot assure you that we will be able to compete
effectively with these industry participants.
 
WE FACE COMPETITION IN LONG DISTANCE MARKETS, PUTTING DOWNWARD PRESSURE ON
  PRICES
 
    We also face intense competition from long distance carriers in the
provision of long distance services, which places downward pressure on prices
for long distance service and makes it difficult for us to achieve positive
operating cash flow. Although the long distance market is dominated by three
major competitors, AT&T, MCI WorldCom and Sprint, hundreds of other companies
also compete in the long distance marketplace. We cannot assure you that we will
be able to effectively compete with any of these industry participants.
 
OUR COMPETITION MAY HAVE SUPERIOR RESOURCES, PLACING US AT A COST AND PRICE
  DISADVANTAGE
 
    Many of our current and potential competitors have financial, personnel and
other resources, including brand name recognition, substantially greater than
those of NEXTLINK. As a result, some of our competitors can raise capital at a
lower cost than we can. Also, our competitors' greater name recognition requires
us to price our services at lower levels in order to win business. Finally, our
competitors' cost advantages give them the ability to reduce their prices for an
extended period of time if they so choose.
 
OUR COMPANY AND INDUSTRY ARE HIGHLY REGULATED, IMPOSING SUBSTANTIAL COMPLIANCE
  COSTS AND RESTRICTING OUR ABILITY TO COMPETE IN OUR TARGET MARKETS
 
    We are subject to varying degrees of federal, state and local regulation.
This regulation imposes substantial compliance costs on us. It also restricts
our ability to compete. For example, in each state in which we desire to offer
our services, we are required to obtain authorization from the appropriate state
commission. We cannot assure you that we will receive authorization for markets
to be launched in the future. For more information, see "Regulation."
 
    The FCC licenses for fixed wireless radio spectrum held by our 50%-owned
affiliate, NEXTBAND, are subject to a petition for reconsideration filed by
another auction participant. The petition asks the FCC to revoke and reauction
 
                                       14
<PAGE>
NEXTBAND's licenses. Because the matter remains pending, we cannot assure you
that the FCC will not grant the petitions and relief sought. Our acquisition of
additional high frequency spectrum from WNP remains subject to FCC approval.
 
THE TECHNOLOGIES THAT WE USE MAY BECOME OBSOLETE, WHICH WOULD LIMIT OR ABILITY
  TO COMPETE EFFECTIVELY
 
    The telecommunications industry is subject to rapid and significant changes
in technology. If we do not replace or upgrade technology and equipment that
becomes obsolete, we will be unable to compete effectively because we will not
be able to meet the expectations of our customers.
 
    The following technology and equipment that we use or will use is subject to
obsolescence: wireline and wireless transmission technologies, circuit,
frame-relay and packet switching technologies and data transmission
technologies, including, the Nortel DMS 500 switches, DSL, ATM, frame-relay and
IP technologies. In addition, we cannot assure you that the technologies that we
choose to invest in will lead to successful implementation of our business plan.
 
WE MAY BE REQUIRED TO PAY PATENT LICENSING FEES, WHICH WILL DIVERT FUNDS WHICH
  COULD BE USED TO MAKE PAYMENTS ON THE NOTES THAT YOU HOLD
 
    From time to time we receive requests to consider licensing certain patents
held by third parties that may have bearing on our interactive voice response
services. Should we be required to pay license fees in the future, such
payments, if substantial, could have a material adverse effect on our results of
operations.
 
IF WE LOSE KEY PERSONNEL AND QUALIFIED TECHNICAL STAFF, OUR ABILITY TO MANAGE
  THE DAY-TO-DAY ASPECTS OF OUR COMPLEX NETWORK WILL BE WEAKENED
 
    We believe that a critical component for our success will be the attraction
and retention of qualified professional and technical personnel. If we lose key
personnel and qualified technical staff, or are unable to recruit qualified
personnel, our ability to manage the day-to-day aspects of our complex network
will be weakened. You should be aware that we face significant competition in
the attraction and retention of personnel who possess the skill sets that we
seek.
 
    In addition, our subsidiaries must also develop and retain a large and
sophisticated sales force. If our subsidiaries do not develop and retain a large
and sophisticated sales force, there will be an adverse effect on our ability to
generate revenue and, consequently, our operating cash flow.
 
CRAIG O. MCCAW, WHO CONTROLS APPROXIMATELY 59% OF NEXTLINK'S VOTING POWER, MAY
  HAVE INTERESTS WHICH ARE ADVERSE TO YOUR INTERESTS
 
    Craig O. McCaw, primarily through his majority ownership and control of
Eagle River Investments, LLC, controls approximately 59% of NEXTLINK's total
voting power. Because Mr. McCaw has the ability to control the direction and
future
 
                                       15
<PAGE>
operations of NEXTLINK, he may make decisions which are adverse to your
interests.
 
    In addition to his investment in NEXTLINK through Eagle River, Mr. McCaw has
significant investments in other communications companies, including Nextel,
Teledesic Corporation and INTERNEXT, some of which could compete with us or act
as one of our suppliers of certain telecommunications services. You should be
aware that we do not have a noncompetition agreement with either Mr. McCaw or
Eagle River. Mr. McCaw is not bound by any contracts with NEXTLINK restricting
his future sales of our common stock.
 
THERE IS NO PUBLIC MARKET FOR THE NEW NOTES, SO YOU MAY BE UNABLE TO SELL NEW
  NOTES
 
    The new notes are new securities for which there is currently no market.
Consequently, the new notes will be relatively illiquid, and you may be unable
to sell your new notes. We do not intend to apply for listing of the new notes
on any securities exchange or for the inclusion of the new notes in any
automated quotation system. Accordingly, we cannot assure you that a liquid
market for the new notes will develop.
 
WE MAY FACE ADDITIONAL COST AND OTHER ADVERSE EFFECTS DUE TO YEAR 2000 ISSUES
 
    To ensure that our computer systems and applications will function properly
beyond 1999, we have implemented a year 2000 program. As part of this program,
we conducted an inventory of network equipment and enterprise systems that
execute primary business processes, such as accounting, service assurance,
service delivery, customer service and billing. We cannot be sure that mission
critical equipment has not been overlooked.
 
    Our determinations whether any systems or applications require modification
or replacement are based in part on statements made to us by vendors as to the
year 2000 compliance of their systems and applications that we use. We will not
be able to independently confirm the accuracy or completeness of these vendor
representations.
 
    Telecommunications and data traffic between our customers who are directly
connected to one of our networks and parties who are not customers of ours are
routed over networks that we do not control. In addition, many of our customers
are connected to one of our networks through facilities of the incumbent local
exchange carrier. Consequently, our customers may not be able to complete calls
or data transmissions if the computer, telecommunications and other systems of
outside entities, including local and interexchange carriers and Internet
service providers that interchange traffic, are not year 2000 compliant. A
failure by some or all of these entities to make their systems year 2000
compliant could create substantial disruptions, which in turn could have a
material adverse effect on our operations.
 
                                       16
<PAGE>
    For further discussion on our year 2000 program, see "Management's
Discussion and Analysis of Financial Condition and Results of Operations--Impact
of Year 2000" in our most recent periodic filing with the Securities and
Exchange Commission.
 
THIS PROSPECTUS INCLUDES FORWARD-LOOKING STATEMENTS
 
    Some statements and information contained in this prospectus are not
historical facts, but are "forward-looking statements", as such term is defined
in the Private Securities Litigation Reform Act of 1995. We wish to caution you
that these forward-looking statements are only predictions, and actual events or
results may differ materially as a result of risks that we face, including those
set forth herein under "Risk Factors." These forward-looking statements can be
identified by the use of forward-looking terminology such as "believes",
"expects", "plans", "may", "will", "would," "could," "should", or "anticipates"
or the negative of these words or other variations of these words or other
comparable words, or by discussions of strategy that involve risks and
uncertainties. Such forward-looking statements include, but are not limited to:
 
    - the number of markets we expect to serve by the end of 2000, the expected
      number of addressable business lines in markets in which we currently
      provide service and the markets in which we expect to provide service by
      the end of 2000;
 
    - our expectations regarding our ability to attract and retain customers;
 
    - our beliefs regarding certain competitive advantages, including that of
      our management structure and provisioning processes and systems;
 
    - our expectation regarding the size of our sales and customer care forces;
 
    - our belief regarding traffic flow over our networks and the effects and
      benefits of high capacity networks with broad coverage based on a uniform
      technology platform;
 
    - our plans to install additional switches, data networking capabilities
      such as frame-relay, IP and ATM facilities, high speed technologies such
      as DSL and wireless technologies;
 
    - our expectation regarding the development of a national network and the
      implementation of a national network end-to-end strategy;
 
    - our anticipated capital expenditures, funding thereof and levels of
      indebtedness and our expectations regarding additional indebtedness;
 
    - statements with respect to our Year 2000 project.
 
                                       17
<PAGE>
                      WHERE YOU CAN FIND MORE INFORMATION
 
    We file annual, quarterly and current reports, proxy statements and other
information with the SEC. We have also filed with the SEC a registration
statement on Form S-4 to register this exchange offer. This prospectus, which
forms part of the registration statement, does not contain all of the
information included in that registration statement. For further information
about NEXTLINK and the new notes offered in this prospectus, you should refer to
the registration statement and its exhibits.
 
    You may read and copy any document we file with the SEC at the SEC's Public
Reference Room at 450 Fifth Street, N.W., Washington, D.C. 20549. Please call
the SEC at 1-800-SEC-0330 for further information on the operation of the Public
Reference Room. We file our SEC materials electronically with the SEC, so you
can also review our filings by accessing the web site maintained by the SEC at
http:// www.sec.gov. This site contains reports, proxy and information
statements and other information regarding issuers that file electronically with
the SEC.
 
    Our principal executive offices are located at 500 108th Avenue N.E., Suite
2200, Bellevue, Washington 98004. Our telephone number is (425) 519-8900.
 
                             DELIVERY OF PROSPECTUS
 
    We remind professional securities dealers of their obligation under the
securities laws to deliver a copy of this prospectus to anyone who buys new
notes from them until June 30, 1999, which is the 90th day after the date of
this prospectus. Securities dealers who were initial purchasers of the old notes
and are acting as underwriters of unsold allotments have additional prospectus
delivery requirements.
 
                                USE OF PROCEEDS
 
    NEXTLINK will not receive any cash proceeds from the issuance of the new
notes as described in this prospectus. NEXTLINK will receive in exchange old
notes in like principal amount. The old notes surrendered in exchange for the
new notes will be retired and canceled and cannot be reissued. Accordingly, the
issuance of the new notes will not result in any change in the indebtedness of
NEXTLINK.
 
                                       18
<PAGE>
                                 CAPITALIZATION
 
                (Dollars in thousands, except per share amounts)
 
    The following table sets forth as of December 31, 1998, the actual
capitalization of NEXTLINK. This table should be read in conjunction with the
Summary Historical Consolidated Financial and Operating Data included elsewhere
in this prospectus, and the audited and unaudited Consolidated Financial
Statements and notes thereto included in the 1998 Form 10-K, which is
incorporated herein by reference.
 
<TABLE>
<CAPTION>
                                                                                                AS OF DECEMBER 31,
                                                                                                       1998
                                                                                                ------------------
<S>                                                                                             <C>
Cash, cash equivalents and marketable securities..............................................    $    1,478,062
Pledged securities(1).........................................................................            21,500
                                                                                                ------------------
    Total.....................................................................................    $    1,499,562
                                                                                                ------------------
                                                                                                ------------------
 
Current portion of long-term obligations......................................................    $        2,755
Other long-term liabilities...................................................................            16,553
12 1/2% Senior Notes due 2006.................................................................           350,000
9 5/8% Senior Notes due 2007..................................................................           400,000
9% Senior Notes due 2008......................................................................           334,379
9.45% Senior Discount notes due 2008..........................................................           428,813
10 3/4% Senior Notes due 2008.................................................................           500,000
                                                                                                ------------------
    Total debt................................................................................         2,032,500
                                                                                                ------------------
Redeemable Preferred Stock, par value $0.01 per share, 25,000,000 shares authorized, net of
  issuance costs:
    14% Preferred Shares, 7,254,675 shares issued and outstanding.............................           361,956
    6 1/2% Cumulative Convertible Preferred Stock, 4,000,000 shares issued and outstanding....           194,212
Shareholders' deficit:
  Common Stock, par value $.02 per share, stated at amounts paid in; Class A, 110,334,000
    shares authorized, 24,170,117 issued and outstanding; Class B, 44,133,600 shares
    authorized, 30,297,902 shares issued and outstanding(2)...................................           354,525
  Deferred compensation.......................................................................           (11,370)
  Accumulated deficit.........................................................................          (589,618)
                                                                                                ------------------
    Total shareholders' deficit...............................................................          (246,463)
                                                                                                ------------------
    Total capitalization......................................................................    $    2,342,205
                                                                                                ------------------
                                                                                                ------------------
</TABLE>
 
- ---------------------
 
(1) Pledged U.S. Treasury securities, which represent funds sufficient to
    provide for payment in full of interest through April 15, 1999 on NEXTLINK's
    12 1/2% Senior Notes due April 15, 2006.
 
(2) Issued and outstanding does not include 9,816,296 and 654,858 shares of
    Class A Common Stock and Class B Common Stock, respectively, issuable upon
    exercise of outstanding options.
 
                                       19
<PAGE>
                                    BUSINESS
 
    Craig O. McCaw founded NEXTLINK in 1994 and is our largest and controlling
shareholder. We provide telephone and other telecommunications and data services
to our targeted customer base of small and medium-sized businesses using our own
electronics and, where practical, our own network facilities, to route telephone
calls and data communications, such as facsimile transmissions, to their final
destination. We were one of the first companies to take advantage of the
Telecommunications Act of 1996, which opened the market for local
telecommunications services to competition. In the language of the 1996 Act, we
are referred to as a "competitive local exchange carrier" or "CLEC." We compete
in each of our markets principally against the dominant telephone company in
that area that had a virtual monopoly on local voice service prior to the entry
of CLECs. We offer our customers high quality local, long distance, data and
enhanced services at competitive prices. We provide these services individually
and as bundled packages, such as a combined package of local and long distance
services. We also are developing a national network strategy to enable us to
offer our customers complete, end-to-end voice and data communications services
over facilities we control.
 
    We develop and operate high capacity, local fiber optic networks with broad
market coverage in a growing number of markets across the United States. We
currently operate 23 individual networks of telephone lines and electronics, and
provide local, long distance, data and enhanced services in 38 markets in 14
states. We serve larger markets, including New York, Los Angeles, Chicago,
Atlanta, the San Francisco Bay Area, Denver, Dallas and Miami, medium-sized
markets, such as Salt Lake City and Nashville, and clusters of smaller markets
in Orange County, California and central Pennsylvania.
 
    In the markets where we provide switched local telecommunications services,
we offer our customers a bundled package of local and resold long distance
services. In these same local markets we also offer customers dedicated
transmission lines for their sole use, as well as direct access to our networks
to long distance carriers and other end users. Our target customer base within
our markets is small and medium-sized businesses, generally those businesses
with fewer than 50 telephone lines. Based on consultants' reports, we estimate
that as of year end 1997, there were approximately 170 million access lines
nationwide, including approximately 55 million business lines.
 
    Our customer base has been growing rapidly, as the following table
demonstrates:
 
<TABLE>
<CAPTION>
                                                                                                 TOTAL ACCESS LINES
DATE                                                                   MARKETS IN SERVICE             INSTALLED
- -------------------------------------------------------------------  -----------------------  -------------------------
<S>                                                                  <C>                      <C>
December 31, 1996..................................................                 7                     8,511
December 31, 1997..................................................                25                    50,131
December 31, 1998..................................................                37                   174,182
</TABLE>
 
                                       20
<PAGE>
    We have also improved our quarterly rate of access line installations. The
following table illustrates this improvement:
 
<TABLE>
<CAPTION>
                                                                                                  ACCESS LINE
                                                                                                 INSTALLATIONS
PERIOD                                                                                            PER QUARTER
- ------------------------------------------------------------------------------------------  -----------------------
<S>                                                                                         <C>
Fourth Quarter 1996.......................................................................             1,604
Fourth Quarter 1997.......................................................................            19,187
Fourth Quarter 1998.......................................................................            40,075
</TABLE>
 
    Based on our recent successes in operating and expanding our existing
networks, as well as new opportunities in other markets, we are pursuing an
aggressive growth plan. We intend to develop networks throughout a majority of
the nation's top 30 markets and to serve markets with 27 million addressable
business lines by the end of 2000. The next phase of our expansion plan includes
the launch of switched service in Washington, D.C. and Seattle in the second
quarter of 1999. We plan to enter other large and medium-sized markets on a
stand-alone basis where economic, competitive and other market factors warrant
such entry, and will consider pursuing smaller markets where we can extend or
cluster an existing network with relatively little incremental capital.
 
    Several recent transactions, described in more detail below, have laid the
foundation for a substantial expansion of our ability to offer a more customers
complete, end-to-end voice and data communications services over our own
facilities.
 
    We believe that a critical factor in the successful implementation of our
strategy is the quality of our management team and their extensive experience in
the telecommunications industry. NEXTLINK has built a management team that we
believe is well suited to challenge the dominant carriers in the local exchange
market. Craig O. McCaw, NEXTLINK's founder and largest and controlling
shareholder, Steven W. Hooper, NEXTLINK's Chairman of the Board and Chief
Executive Officer Wayne M. Perry, NEXTLINK's Vice Chairman and George M.
Tronsrue III, NEXTLINK's President and Chief Operating Officer, each has 16 or
more years of experience in leading companies in competitive segments of the
telecommunications industry. In addition, the presidents of NEXTLINK's operating
subsidiaries and NEXTLINK's senior officers have an average of 18 years of
experience in the telecommunications industry. Mr. Hooper and Mr. Perry were
members of the senior management team at McCaw Cellular Communications, Inc.
during the years in which it became the nation's largest cellular telephone
company. Following McCaw Cellular's sale to AT&T in 1994, Mr. Perry was Vice
Chairman of AT&T Wireless Services, Inc. and Mr. Hooper was Chief Executive
Officer of AT&T Wireless Services.
 
BUSINESS STRATEGY
 
    We have built a customer-focused, locally oriented organization dedicated to
providing local and long distance telephone services at competitive prices to
small and medium-sized businesses. Our goal is maximize penetration of our
targeted customer
 
                                       21
<PAGE>
base and to become a leading provider of end-to-end voice and data
communications services.
 
    - DEVELOP FIBER OPTIC NETWORKS. We build high-capacity local networks in the
      central business districts of our targeted markets using fiber optic cable
      bundles, which are capable of carrying high volumes of voice, data, video
      and Internet traffic as well as other high bandwidth services. This
      enables us to provide direct connections to a high percentage of
      commercial buildings and local telephone company switching offices located
      near our network. We design our networks to maximize the proportion of our
      traffic that is both originated and terminated on our own networks, to
      give us higher long-term operating margins.
 
    - USE WIRELESS SPECTRUM TO CONNECT CUSTOMERS DIRECTLY TO OUR NETWORKS. To
      connect customers to our networks, we currently use data direct
      connections to buildings where customers are located and unbundled loop
      lines leased from the incumbent carrier. As an alternative, we are also
      developing the means to make wireless connections between our fiber
      networks and off-net customers.
 
    - LINK OUR OPERATIONS IN EACH CITY TO ONE ANOTHER. We are developing a
      national strategy that will link our local networks to each other using
      our interest in a national fiber optic network that is expected to link 50
      cities in the United States and Canada. This network, which is now under
      construction, is designed to support voice and data services.
 
    - CONTINUE MARKET EXPANSION. We plan to build our own local facilities-based
      networks throughout a majority of the nation's top 30 markets and to
      provide service in markets with a total of 27 million addressable business
      lines by the end of 2000.
 
    - DEPLOY ADVANCED TECHNOLOGIES FOR USE IN DATA COMMUNICATIONS.We are
      developing plans for deploying new technologies which will route data
      communications to their final destination efficiently and at high speeds.
      These technologies include Asynchronous Transfer Mode, or ATM, Internet
      Protocol, or IP frame-relay facilities, and Digital Subscriber Line, or
      DSL services. To date, our local networks have been used primarily for
      traditional circuit-switched technologies through our Nortel DMS 500
      switches. Our fiber networks have been designed, however, to support the
      introduction of additional technologies for the switching and transmission
      of data services. Our networks have also been designed to allow voice,
      data and all network applications to be carried over a single
      infrastructure using an IP based architecture. We anticipate that these
      newer technologies will allow us to provide a full range of data services
      more efficiently and cost effectively over our networks, while continuing
      to provide traditional circuit switched voice services to our customers.
 
    - CONTINUE TO FOSTER DECENTRALIZED LOCAL MANAGEMENT AND CONTROL. We have
      recruited experienced entrepreneurs and industry executives as presidents
      of
 
                                       22
<PAGE>
      each of our regional groups of operating subsidiaries, many of whom have
      previously built and led their own start-up telecommunications businesses.
      We believe that this local management focus will provide a critical
      competitive edge in customer acquisition and retention in each market.
 
    - FOCUS SALE EFFORTS ON SMALL AND MEDIUM-SIZED BUSINESS. We believe that the
      incumbent local telephone companies are less likely to apply significant
      resources towards retaining businesses and professional groups that have
      fewer than 50 access lines, the group on which we currently focus our
      sales efforts.
 
    - ASSIGNED CUSTOMER CARE REPRESENTATIVES TO EACH CUSTOMER. We assign a
      single customer care representative to each customer. Each representative
      is responsible for solving problems and responding to inquires from their
      assigned customers.
 
    - CONTINOUSLY IMPROVE TRANSITIONING OF NEW CUSTOMERS ONTO OUR NETWORK.
      Because the process of the transitioning a new customer from the incumbent
      company's network is complex, we continue to identify and implement
      practices to make the process rapid and seamless, including implementation
      of a comprehensive information technology platform.
 
                              RECENT TRANSACTIONS
 
INTERNEXT
 
    In July 1998, we announced the formation of INTERNEXT L.L.C. NEXTLINK and
Eagle River Investments, L.L.C. each beneficially owns 50% of INTERNEXT. Eagle
River is the holding company, owned principally by Craig O. McCaw, that is our
largest shareholder. INTERNEXT has entered into a cost sharing agreement with
Level 3 Communications, Inc. Level 3 is constructing a national fiber optic
network that is expected to cover more than 16,000 route miles with six or more
conduits and connect 50 cities in the United States and Canada.
 
    INTERNEXT has an exclusive interest in 24 fibers in a shared, filled conduit
throughout this network, and also has an exclusive interest in one empty conduit
and the right to 25% of the fibers pulled through the sixth and any additional
conduits in the network.
 
    INTERNEXT has a $700 million commitment under the cost sharing agreement,
which is payable largely as segments of the network are built out and accepted
by INTERNEXT. INTERNEXT expects the network build-out to occur substantially in
years 2000 and 2001. We have guaranteed 50% of the financial obligations of
INTERNEXT under the cost sharing agreement. Together with Eagle River, we also
have guaranteed the performance of other obligations of INTERNEXT under the cost
sharing agreement.
 
                                       23
<PAGE>
NEXTBAND
 
    NEXTLINK and Nextel Communications, Inc., a wireless telecommunications
company in which Eagle River holds a substantial interest, each owns 50% of
NEXTBAND Communications, L.L.C. NEXTBAND acquired high-frequency radio spectrum
licenses for 42 markets covering approximately 114 million persons located
within the licensed areas through a FCC-sponsored auction. We have reached an
agreement in principle with Nextel to acquire Nextel's 50% interest in NEXTBAND.
Nextband's FCC licences are in the Local Multipoint Distribution Service, or
LMDS, which is a newly authorized fixed broadband service that the license
holder may use to provide wireless local telephone service, wireless
transmission of telephone calls in bulk quantity, high-speed data transfer,
video broadcasting and videoconferencing, in any combination. We are evaluating
means to use our access to NEXTBAND's LMDS spectrum to enhance our ability to
connect customers to our fiber rings and to deploy fixed wireless telephony
technologies using LMDS spectrum, where we determine that it is cost effective
to do so. Our acquisition of Nextel's interest in NEXTBAND will be subject to
certain conditions, including approval by the Federal Communications Commission.
 
ACQUISITION OF WNP COMMUNICATIONS, INC.
 
    On January 14, 1999, we entered into an agreement to acquire WNP
Communications, Inc. for approximately $695 million, payable in cash and our
Class A Common Stock. Of this amount, approximately $152.9 million will be paid
to the FCC for license fees, including interest thereon. Substantially all of
WNP's assets consist of recently-issued LMDS licenses. By acquiring WNP, we will
receive 39 A block LMDS wireless licenses covering an area where 92 million
people live or work and one B block LMDS wireless license covering an area where
16 million people live or work. After combining the wireless LMDS licenses that
we have agreed to acquire from WNP with the licenses that we own through our
interest in NEXTBAND, we will become the largest holder of LMDS wireless
spectrum in North America, covering approximately 95 percent of the individuals
in the 30 largest markets in the United States. Our acquisition of WNP is
subject to certain conditions, including approval by the Federal Communications
Commission.
 
COVAD STRATEGIC ALLIANCE
 
    On January 4, 1999, we announced a strategic agreement with Covad
Communications Group, Inc., a leading provider of high-speed digital
communication services using DSL technology. DSL technology is designed to
overcome performance bottlenecks of the existing public switched telephone
networks by increasing the data carrying capacity of copper telephone lines.
Under this agreement, we have invested $20 million in Covad. In addition, Covad
will become a preferred provider of DSL services to NEXTLINK. NEXTLINK will also
be a preferred provider to Covad for local transport and collocation services
for Covad's regional data centers.
 
                                       24
<PAGE>
MANAGEMENT
 
    At its meeting on June 4, 1998, our board of directors amended NEXTLINK's
bylaws to increase the size of the board from nine to ten persons. At that
meeting, our board appointed Gregory J. Parker to fill the new vacancy. Mr.
Parker, who is 41 years old, is President of Ampersand Holdings, Inc., a holding
company that manages the investments of Wendy P. McCaw. He was a partner of the
law firm of Seed, Mackall & Cole LLP from 1990 to 1998, where his practice
emphasized financing, capital investment and real estate matters. From 1994 to
1997, he was Managing Partner of the firm. Mr. Parker also is the trustee of The
Ampersand Telecom Trust. Ampersand Telecom, LLC owns 9,722,649 shares of our
Class B Common Stock. Ampersand Telecom LLC's holdings represent 33% of the
outstanding shares of our Class B Common Stock, 18% of the total outstanding
shares of our common stock, and 31% of the total voting power of our outstanding
common stock. The Ampersand Telecom Trust is the Managing Member of Ampersand
Telecom, LLC. The beneficiary of The Ampersand Telecom Trust is Wendy P. McCaw.
 
    Effective March 26, 1999, Steven W. Hooper, the chairman of our board of
directors, became our chief executive officer. He replaced Wayne Perry, our
former chief executive officer and vice chairman. Mr. Perry has retained his
position as vice chairman. Mr. Hooper continues to serve as chairman of our
board.
 
    Effective July 17, 1998, James F. Voelker resigned as President and from our
board of directors. Our board of directors elected George M. Tronsrue, III, who
had been serving as NEXTLINK's Chief Operating Officer, to the additional office
of President, but has not filled the board of directors vacancy resulting from
Mr. Voelker's resignation.
 
    Effective January 21, 1999, Scot Jarvis resigned from our board of
directors. At its February 4, 1999 meeting, our board of directors appointed
Nicolas Kauser to our board of directors to fill the vacancy created by the
resignation of Mr. Jarvis. From 1994 until his recent retirement, Mr. Kauser was
Executive Vice President and Chief Technology Officer of AT&T Wireless Services.
From 1990 until 1994, Mr. Kauser was Chief Technology Officer of McCaw Cellular,
which merged with AT&T Wireless in 1994.
 
                                       25
<PAGE>
                                   REGULATION
 
    The federal Telecommunications Act of 1996 opened local telephone markets to
competition from companies like NEXTLINK. Prior to that time, states typically
granted an exclusive franchise in each local service area to a single dominant
carrier-- often a former subsidiary of AT&T known as a "Baby Bell"--which owned
and operated the entire local exchange network. The 1996 Act preserved state and
local jurisdiction over many aspects of local telephone service, and, as a
result, NEXTLINK is subject to varying degrees of federal, state and local
regulation. FCC and state regulators, and other legislative or judicial
initiatives relating to the telecommunications industry, could help or hinder
our business.
 
    We are not currently required to obtain FCC authorization for the
installation, acquisition or operation of our wireline network facilities. We
are required to hold and we have obtained FCC authorizations for the operation
of our wireless facilities. In each state in which we desire to offer our
services, we also must first obtain authorization from the appropriate state
commission. Although we currently hold the required state authorizations in each
of our operational markets, we can't be certain that we will receive the
necessary state authorizations for markets to be launched in the future.
 
    Unlike the incumbent carriers, we are not currently subject to price cap or
rate of return regulation, which leaves us more free to set our own pricing
policies. The FCC requires us to file interstate tariffs on an ongoing basis for
interstate and international interexchange traffic. An FCC order that would have
exempted us from any requirement to file tariffs for interstate access and
domestic long distance service has been stayed pending further judicial review,
and, as a result, we currently file tariffs for these services. Our intrastate
services are also generally subject to state certification and tariff or price
list filing requirements.
 
    The 1996 Act gave the FCC significant responsibility for its implementation,
especially in the areas of universal service, access charges, numbering, number
portability and price caps. The details of the rules adopted by the FCC, and the
extent to which they are upheld by the courts reviewing the FCC's rules, will
have a significant effect on when and to what extent barriers to competition in
local services are removed. For example, the FCC has the power to grant
incumbent carriers increased flexibility to enable them to reduce prices for
special access, private line services and advanced telecommunications services.
 
    The 1996 Act provides incentives to most of the incumbent carriers to enter
into interconnection agreements with carriers like NEXTLINK. We need
interconnection agreements to gain access to the incumbent carriers' networks.
Although we have interconnection agreements in all of our currently operational
markets, we can't be certain that incumbent carriers in new markets we seek to
enter will negotiate quickly with us or that any resulting agreements will be on
terms favorable to us.
 
                                       26
<PAGE>
    The incumbent carriers have frequently resorted to litigation in an attempt
to obtain the benefits of these incentives without offering consumers and
competitors like NEXTLINK the full benefits intended by the 1996 Act. For
example, in September 1998, the FCC ruled that certain incumbent carrier
"teaming" arrangements with long distance carriers, which would have allowed
incumbent carriers to offer a form of "one stop shopping" in competition with
NEXTLINK's combined local and long distance offerings, violated the 1996 Act. In
response, the incumbent carriers have filed petitions with the United States
Court of Appeals for the District of Columbia seeking to overturn this ruling.
If this FCC's ruling is reversed by the courts, one of our current competitive
advantages would be undermined.
 
    In January 1999, the U.S. Supreme Court upheld key provisions of the FCC
rules implementing the 1996 Act, in a decision that was generally favorable to
competitive telephone companies like NEXTLINK. In two earlier decisions, the
United States Court of Appeals for the Eighth Circuit had invalidated these
rules. The Supreme Court's decision reinstated all but one of the FCC rules
invalidated by the Eighth Circuit. The Supreme Court held that the FCC has
general jurisdiction to implement the 1996 Act's local competition provisions,
including pricing and enforcement jurisdiction. Significantly, the Court upheld
that the FCC's "pick and choose" rule, which allows competitors to choose which
provisions of other carriers' interconnection agreements they wish to
incorporate in their own interconnection agreements with that incumbent carrier.
 
    A key provision of the 1996 Act requires incumbent carriers to make elements
of their networks available to competing carriers like NEXTLINK at reasonable
rates. The Supreme Court broadly affirmed these provisions, but held that the
FCC did not correctly determine precisely which network elements must be
unbundled and made available to competitors like NEXTLINK. This ruling cast
existing interconnection agreements in doubt when some incumbent carriers stated
that they would no longer make elements of their networks available until the
FCC clarified which elements they must offer to competitors. These incumbent
carriers subsequently assured FCC officials that they would continue to provide
currently available network elements to their competitors and continue to
negotiate new interconnection agreements in good faith.
 
    Until the FCC adopts new rules complying with the Supreme Court's decision,
competitors like NEXTLINK will need to rely to a great extent on the continued
good faith of the incumbent carriers, rather than express regulatory rights, to
obtain new interconnection agreements and network elements.
 
    The Supreme Court decision did not address or resolve the incumbent
carriers' challenge to the FCC's forward-looking pricing methodology for
unbundled network elements. The incumbent carriers have challenged this
methodology, claiming that any correct procedure would take into account
historical costs. If the incumbent carriers succeed in this contention, we would
have to pay more to purchase network elements, which could significantly
increase our cost of doing business.
 
                                       27
<PAGE>
                               THE EXCHANGE OFFER
 
BACKGROUND
 
    NEXTLINK originally sold the outstanding 10 3/4% Senior Notes due 2008 on
November 12, 1998 in a transaction exempt from the registration requirements of
the Securities Act. Salomon Smith Barney Inc., as the initial purchaser,
subsequently resold the notes to qualified institutional buyers in reliance on
Rule 144A and under Regulation S under the Securities Act. As of the date of
this prospectus, $500.0 million aggregate principal amount of unregistered notes
are outstanding.
 
    NEXTLINK and Salomon Smith Barney Inc. entered into a registration rights
agreement under which NEXTLINK agreed that it would, at its own cost,
 
    - file an exchange offer registration statement under the Securities Act
      within 90 days after November 12, 1998, the original issue date of the old
      notes, and
 
    - use its reasonable best efforts to cause the exchange offer registration
      statement to become effective under the Securities Act at the earliest
      possible time, but no later than 120 days following November 12, 1998.
 
    The summary in this prospectus of provisions of the registration rights
agreement does not purport to be complete and is subject to, and is qualified in
its entirety by, all the provisions of the registration rights agreement, a copy
of which is filed as an exhibit to the registration statement of which this
prospectus is a part.
 
RESALE OF THE NEW NOTES
 
    Based on no-action letters issued by the staff of the Securities and
Exchange Commission to third parties, NEXTLINK believes that a holder of old
notes, but not a holder who is an affiliate of NEXTLINK within the meaning of
Rule 405 of the Securities Act, who exchanges old notes for new notes in the
exchange offer, generally may offer the new notes for resale, sell the new notes
and otherwise transfer the new notes without further registration under the
Securities Act and without delivery of a prospectus that satisfies the
requirements of Section 10 of the Securities Act. This does not apply, however,
to a holder who is an affiliate of NEXTLINK within the meaning of Rule 405 of
the Securities Act. NEXTLINK also believes that a holder may offer, sell or
transfer the new notes only if the holder acquires the new notes in the ordinary
course of its business and is not participating, does not intend to participate
and has no arrangement or understanding with any person to participate in a
distribution of the new notes.
 
    Any holder of old notes using the exchange offer to participate in a
distribution of new notes cannot rely on the no-action letters referred to
above. This includes a broker-dealer that acquired old notes directly from
NEXTLINK, but not as a result of market-making activities or other trading
activities. Consequently, the holder must comply with the registration and
prospectus delivery requirements of the Securities Act in the absence of an
exemption from such requirements.
 
                                       28
<PAGE>
    Each broker-dealer that receives new notes for its own account in exchange
for old notes, where such old notes were acquired by the broker-dealer as a
result of market-making activities or other trading activities may be a
statutory underwriter and must acknowledge that it will deliver a prospectus
meeting the requirements of the Securities Act in connection with the resale of
new notes received in exchange for old notes. The letter of transmittal which
accompanies this prospectus states that by so acknowledging and by delivering a
prospectus, a participating broker-dealer will not be deemed to admit that it is
an underwriter within the meaning of the Securities Act. A participating
broker-dealer may use this prospectus, as it may be amended from time to time,
in connection with resales of new notes it receives in exchange for old notes in
the exchange offer. NEXTLINK will make this prospectus available to any
participating broker-dealer in connection with any resale of this kind for a
period of 30 days after the expiration date of the exchange offer. See "Plan of
Distribution".
 
    Each holder of the old notes who wishes to exchange old notes for new notes
in the exchange offer will be required to represent and acknowledge, for the
holder and for each beneficial owner of such old notes, whether or not the
beneficial owner is the holder, in the letter of transmittal that:
 
    - the new notes to be acquired by the holder and each beneficial owner, if
      any, are being acquired in the ordinary course of business,
 
    - neither the holder nor any beneficial owner is an affiliate, as defined in
      Rule 405 of the Securities Act, of NEXTLINK or any of its subsidiaries,
 
    - any person participating in the exchange offer with the intention or
      purpose of distributing new notes received in exchange for old notes,
      including a broker-dealer that acquired old notes directly from NEXTLINK,
      but not as a result of market-making activities or other trading
      activities cannot rely on the no-action letters referenced above and must
      comply with the registration and prospectus delivery requirements of the
      Securities Act, in connection with a secondary resale of the new notes
      acquired by such person,
 
    - if the holder is not a broker-dealer, the holder and each beneficial
      owner, if any, are not participating, do not intend to participate and
      have no arrangement or understanding with any person to participate in any
      distribution of the new notes received in exchange for old notes, and
 
    - if the holder is a broker-dealer that will receive new notes for the
      holder's own account in exchange for old notes, the old notes to be so
      exchanged were acquired by the holder as a result of market-making or
      other trading activities and the holder will deliver a prospectus meeting
      the requirements of the Securities Act in connection with any resale of
      such new notes received in the exchange offer. However, by so representing
      and acknowledging and by delivering a prospectus, the holder will not be
      deemed to admit that it is an underwriter within the meaning of the
      Securities Act.
 
                                       29
<PAGE>
SHELF REGISTRATION STATEMENT
 
    If applicable law or interpretations of the staff of the SEC are changed so
that the new notes received by holders who make all of the above representations
in the letter of transmittal are not or would not be, upon receipt,
transferrable by each such holder without restriction under the Securities Act,
NEXTLINK will, at its cost:
 
    - file a shelf registration statement covering resales of the old notes,
 
    - use its reasonable best efforts to cause the shelf registration statement
      to be declared effective under the Securities Act at the earliest possible
      time, but no later than 120 days after November 12, 1998, and
 
    - use its reasonable best efforts to keep effective the shelf registration
      statement until the earlier of two years after November 12, 1998 or the
      time when all of the applicable old notes are no longer outstanding.
 
    NEXTLINK will, if and when it files the shelf registration statement,
provide to each holder of the old notes copies of the prospectus which is a part
of the shelf registration statement, notify each holder when the shelf
registration statement has become effective and take other actions as are
required to permit unrestricted resales of the old notes. A holder that sells
old notes pursuant to the shelf registration statement generally must be named
as a selling security-holder in the related prospectus and must deliver a
prospectus to purchasers, will be subject to civil liability provisions under
the Securities Act in connection with these sales and will be bound by the
provisions of the registration rights agreement which are applicable to the
holder, including certain indemnification obligations. In addition, each holder
of old notes must deliver information to be used in connection with the shelf
registration statement and provide comments on the shelf registration statement
in order to have its old notes included in the shelf registration statement and
benefit from the provisions regarding any liquidated damages described below.
 
INCREASE IN INTEREST RATE
 
    If NEXTLINK is required to file the shelf registration statement and
 
    (1) either
 
    - the shelf registration statement has not become effective or been declared
      effective on or before the 120th calendar day following November 12, 1998,
      or
 
    - the shelf registration statement has been declared effective and such
      shelf registration statement ceases to be effective, except as
      specifically permitted in the registration rights agreement, without being
      succeeded promptly by an additional registration statement filed and
      declared effective, or
 
                                       30
<PAGE>
    (2) the shelf registration statement has not become effective or been
declared effective on or before the 165th day after November 12, 1998, the
interest rate borne by the old notes will be increased in accordance with the
following table:
 
<TABLE>
<CAPTION>
                                                                              INITIAL INCREASE
                         EVENT                                                IN INTEREST RATE
- --------------------------------------------------------  --------------------------------------------------------
<S>                                                       <C>
1.  Shelf registration statement not declared effective   0.5% per annum following this 120 day period, determined
    on or prior to 120th day following November 12, 1998  daily, from the date of the event, until the date it is
    or shelf registration statement ceases to be          cured.
    effective
2.  Shelf registration statement has not become           Additional 0.25% for each subsequent 90 day period
    effective or been declared effective on or before
    the 165th day after November 12, 1998
</TABLE>
 
    However, in no event will the interest rate borne by the outstanding notes
be increased by an aggregate of more than 1.0%.
 
    The sole remedy available to the holders of the old notes will be the
immediate assessment of cash interest on the old notes as described above. Any
amounts of additional interest due as described above will be payable in cash on
the same interest payments dates as the old notes.
 
TERMS OF THE EXCHANGE OFFER
 
    Upon the exchange offer registration statement being declared effective,
NEXTLINK will offer the new notes in exchange for surrender of the old notes.
NEXTLINK will keep the exchange offer open for at least 30 days, or longer if
required by applicable law, after the date notice of the exchange offer is
mailed to the holders of the old notes.
 
    Upon the terms and subject to the conditions contained in this prospectus
and in the letter of transmittal which accompanies this prospectus, NEXTLINK
will accept any and all old notes validly tendered and not withdrawn before 5:00
p.m., New York City time, on the expiration date of the exchange offer. NEXTLINK
will issue an equal principal amount of new notes in exchange for the principal
amount of old notes accepted in the exchange offer. Holders may tender some or
all of their old notes under the exchange offer. Old notes may be tendered only
in integral multiples of $1,000.
 
    The form and terms of the new notes will be the same as the form and terms
of the old notes except that:
 
    (1) the new notes will have been registered under the Securities Act and
       therefore will not bear legends restricting their transfer, and
 
    (2) the new notes will not contain certain terms providing for an increase
       in the interest rate on the old notes under specific circumstances which
       are described in the registration rights agreement.
 
                                       31
<PAGE>
The new notes will evidence the same debt as the old notes and will be entitled
to the benefits of the indenture governing the old notes.
 
    In connection with the exchange offer, holders of old notes do not have any
appraisal or dissenters' rights under law or the indenture governing the old
notes. NEXTLINK intends to conduct the exchange offer in accordance with the
applicable requirements of the Exchange Act and the rules and regulations of the
Securities and Exchange Commission related to such offers.
 
    NEXTLINK shall be deemed to have accepted validly tendered old notes when,
as and if NEXTLINK has given oral or written notice of acceptance to United
States Trust Company, exchange agent for the exchange offer. The exchange agent
will act as agent for the tendering holders for the purpose of receiving the new
notes from NEXTLINK.
 
    If any tendered old notes are not accepted for exchange because of an
invalid tender, the occurrence of certain other events specified in this
prospectus or if old notes are submitted for a greater principal amount than the
holder desires to exchange, the certificates for the unaccepted old notes will
be returned without expense to the tendering holder. If old notes were tendered
by book-entry transfer in the exchange agent account at The Depository Trust
Company in accordance with the book-entry transfer procedures described below,
these non-exchanged old notes will be credited to an account maintained with The
Depositary Trust Company as promptly as practicable after the expiration date of
the exchange offer.
 
    NEXTLINK will pay all charges and expenses, other than transfer taxes in
certain circumstances, in connection with the exchange offer. See "--Fees and
Expenses." Holders who tender old notes in the exchange offer will therefore not
need to pay brokerage commissions or fees or, subject to the instructions in the
letter of transmittal, transfer taxes with respect to the exchange of old notes
in the exchange offer.
 
EXPIRATION DATE; EXTENSIONS; AMENDMENTS
 
    The expiration date of the exchange offer is 5:00 p.m., New York City time,
on May 3, 1999, unless NEXTLINK, in its reasonable discretion, extends the
exchange offer, in which case the expiration date shall be the latest date and
time to which the exchange offer is extended.
 
    In order to extend the exchange offer, NEXTLINK will notify the exchange
agent of any extension by oral or written notice and will make a public
announcement of the extension before 9:00 a.m., New York City time, on the next
business day after the previously scheduled expiration date.
 
    NEXTLINK reserves the right, in its reasonable discretion:
 
    - to delay accepting any old notes, to extend the exchange offer or to
      terminate the exchange offer if, in its reasonable judgement, any of the
      conditions
 
                                       32
<PAGE>
      described below under "--Conditions" shall not have been satisfied, by
      giving oral or written notice of the delay, extension or termination to
      the exchange agent, or
 
    - to amend the terms of the exchange offer in any manner.
 
    NEXTLINK will promptly announce any such event making a timely release to
Dow Jones News Service and may or may not do so by other means as well.
 
PROCEDURES FOR TENDERING
 
    You may tender your own old notes in the exchange offer. To tender in the
exchange offer, a holder must do the following:
 
    - complete, sign and date the letter of transmittal, or a facsimile of the
      letter of transmittal,
 
    - have the signatures thereon guaranteed if required by the letter of
      transmittal, and
 
    - except as discussed in "--Guaranteed Delivery Procedures," mail or
      otherwise deliver the letter of transmittal, or facsimile, together with
      the old notes and any other required documents, to the exchange agent
      prior to 5:00 p.m., New York City time, on the expiration date of the
      exchange offer.
 
    The exchange agent must receive the old notes, a completed letter of
transmittal and all other required documents at the address listed below under
"--Exchange Agent" before 5:00 p.m., New York City time, on the expiration date
for the tender to be effective. You may deliver your old notes by using the
book-entry transfer procedures described below, as long as the exchange agent
receives confirmation of the book-entry transfer before the expiration date.
 
    The Depository Trust Company has authorized its participants that hold old
notes on behalf of beneficial owners of old notes through The Depository Trust
Company to tender their old notes as if they were holders. To effect a tender of
old notes, The Depository Trust Company participants should either:
 
    (1) complete and sign the letter of transmittal (or a manually signed
       facsimile of the letter), have the signature thereon guaranteed if
       required by the instructions to the letter of transmittal, and mail or
       deliver the letter of transmittal (or the manually signed facsimile) to
       the exchange agent according to the procedure described in "Procedures
       for Tendering" or
 
    (2) transmit their acceptance to The Depository Trust Company through its
       automated tender offer program for which the transaction will be eligible
       and follow the procedure for book-entry transfer its described in
       "--Book-Entry Transfer."
 
    By tendering, each holder will make the representations contained in the
fourth paragraph above under the heading "--Resale of the New Notes." Each
participating
 
                                       33
<PAGE>
broker-dealer must acknowledge that it will deliver a prospectus in connection
with any resale of such new notes. See "Plan of Distribution."
 
    The tender by a holder and the acceptance of the tender by NEXTLINK will
constitute the agreement between the holder and NEXTLINK set forth in this
prospectus and in the letter of transmittal.
 
    THE METHOD OF DELIVERY OF OLD NOTES AND THE LETTER OF TRANSMITTAL AND ALL
OTHER REQUIRED DOCUMENTS TO THE EXCHANGE AGENT IS AT THE ELECTION AND SOLE RISK
OF THE HOLDER. AS AN ALTERNATIVE TO DELIVERY BY MAIL, HOLDERS MAY WISH TO
CONSIDER OVERNIGHT OR HAND DELIVERY SERVICE. IN ALL CASES, HOLDERS SHOULD ALLOW
SUFFICIENT TIME TO ASSURE DELIVERY TO THE EXCHANGE AGENT BEFORE THE EXPIRATION
DATE. NO LETTER OF TRANSMITTAL OR OLD NOTES OR BOOK-ENTRY CONFIRMATION SHOULD BE
SENT TO NEXTLINK. HOLDERS MAY REQUEST THEIR RESPECTIVE BROKERS, DEALERS,
COMMERCIAL BANKS, TRUST COMPANIES OR NOMINEES TO EFFECT THE ABOVE TRANSACTIONS
ON THEIR BEHALF.
 
    Any beneficial owner whose old notes are registered in the name of a broker,
dealer, commercial bank, trust company or other nominee and who wishes to tender
should contact the registered holder promptly and instruct it to tender on the
beneficial owner's behalf. See "Instructions to Registered Holder and/or
Book-Entry Transfer Facility Participant from Beneficial Owner" included with
the letter of transmittal. If the beneficial owner wishes to tender on his own
behalf, such owner must, prior to completing and executing the letter of
transmittal and delivering such beneficial owner's old notes, either make
appropriate arrangements to register ownership of the old notes in such owner's
name or obtain a properly completed bond power from the registered holder. The
transfer of registered ownership may take considerable time.
 
    Signatures on a letter of transmittal or a notice of withdrawal must be
guaranteed by an eligible guarantor institution (within the meaning of Rule 17A
d-5 under the Exchange Act) unless the old notes are tendered:
 
    - by a registered holder who has not completed the box entitled "Special
      Issuance Instructions" or "Special Delivery Instructions" on the letter of
      transmittal, or
 
    - for the account of an eligible guarantor institution.
 
    If signatures on a letter of transmittal or a notice of withdrawal, as the
case may be, are required to be guaranteed, the guarantee must be by a member
firm of a registered national securities exchange or of the National Association
of Securities Dealers, Inc., a commercial bank or trust company having an office
or correspondent in the United States or an eligible guarantor institution.
 
    If a letter of transmittal is signed by a person other than the registered
holder of any old notes listed in the letter of transmittal, the old notes must
be endorsed or accompanied by a properly completed bond power and signed by the
registered holder as the registered holder's name appears on the old notes.
 
                                       34
<PAGE>
    If a letter of transmittal or any old notes or bond powers are signed by
trustees, executors, administrators, guardians, attorneys-in-fact, officers of
corporations or others acting in a fiduciary or representative capacity, such
persons should so indicate when signing, and unless waived by NEXTLINK, evidence
satisfactory to NEXTLINK of their authority to so act must be submitted with the
letter of transmittal.
 
    Promptly after the date of this prospectus, the exchange agent will
establish a new account or utilize an existing account with respect to the old
notes at the book-entry transfer facility, The Depository Trust Company, for the
purpose of facilitating the exchange offer. Subject to the establishment of the
accounts, any financial institution that is a participant in the book-entry
transfer facility's system may make book-entry delivery of old notes by causing
the book-entry transfer facility to transfer the old notes into the exchange
agent's account with respect to the old notes in accordance with that facility's
procedures. Although delivery of the old notes may be effected through
book-entry transfer into the exchange agent's account at the book-entry transfer
facility, an appropriate letter of transmittal properly completed and duly
executed or an agent's message with any required signature guarantee and all
other required documents the exchange agent at its address listed below on or
before the expiration date of the exchange offer, or, if the guaranteed delivery
procedures described below are complied with, within the time period provided
under such procedures. Delivery of documents to the book-entry transfer facility
does not constitute delivery to the exchange agent.
 
    The term "agent's message" means a message transmitted by The Depositary
Trust Company to, and received by, the exchange agent, which states that The
Depository Trust Company has received an express acknowledgment from the
participant in The Depository Trust Company tendering the old notes stating:
 
    - the aggregate principal amount of old notes which have been tendered by
      such participant,
 
    - that such participant has received and agrees to be bound by the term of
      the letter of transmittal and
 
    - that NEXTLINK may enforce such agreement against the participant.
 
    All questions as to the validity, form, eligibility (including time of
receipt), acceptance of tendered old notes and withdrawal of tendered old notes
will be determined by NEXTLINK in its sole discretion, which determination will
be final and binding. NEXTLINK reserves the absolute right to reject any and all
old notes not properly tendered or any old notes NEXTLINK's acceptance of which
would, in the opinion of counsel for NEXTLINK, be unlawful. NEXTLINK also
reserves the right to waive any defects, irregularities or conditions of tender
as to particular old notes. NEXTLINK's interpretation of the terms and
conditions of the exchange offer, including the instructions in the letter of
transmittal, will be final and binding on all parties. Unless waived, any
defects or irregularities in connection with tenders of old notes must be cured
within a period of time that NEXTLINK shall determine.
 
                                       35
<PAGE>
Neither NEXTLINK, the exchange agent nor any other person shall incur any
liability for failure to give notice of any defect or irregularity with respect
to any tender of old notes. Tenders of old notes will not be deemed to have been
made until such defects or irregularities mentioned above have been cured or
waived. Any old notes received by the exchange agent that are not properly
tendered and as to which the defects or irregularities have not been cured or
waived will be returned by the exchange agent to the tendering holders, unless
otherwise provided in the letter of transmittal, as soon as practicable
following the expiration date of the exchange offer.
 
GUARANTEED DELIVERY PROCEDURES
 
    A holder who wishes to tender its old notes and:
 
        - whose old notes are not immediately available,
 
        - who cannot deliver the holder's old notes, the letter of transmittal
          or any other required documents to the exchange agent prior to the
          expiration date, or
 
        - who cannot complete the procedures for book-entry transfer, before the
          expiration date,
 
    may effect a tender if:
 
        - the tender is made through an eligible guarantor institution,
 
        - before the expiration date, the exchange agent receives from the
          eligible guarantor institution a properly completed and duly executed
          notice of guaranteed delivery by facsimile transmission, mail or hand
          delivery, the name and address of the holder, the certificate
          number(s) of the old notes and the principal amount of old notes
          tendered, stating that the tender is being made thereby and
          guaranteeing that, within three New York Stock Exchange trading days
          after the expiration date, the letter of transmittal (or facsimiles
          thereof) together with the certificate(s) representing the old notes
          (or a confirmation of book-entry transfer of the old notes into the
          exchange agent's account at the book-entry transfer facility), and any
          other documents required by the letter of transmittal will be
          deposited by the eligible guarantor institution with the exchange
          agent, and
 
        - the exchange agent receives, within three New York Stock Exchange
          trading days after the expiration date, a properly completed and
          executed letter of transmittal or facsimile, as well as the
          certificate(s) representing all tendered old notes in proper form for
          transfer or a confirmation of book-entry transfer of such old notes
          into the exchange agent's account at the book-entry transfer facility,
          and all other documents required by the letter of transmittal.
 
                                       36
<PAGE>
WITHDRAWAL OF TENDERS
 
    Except as otherwise provided in this prospectus, tenders of old notes may be
withdrawn at any time prior to 5:00 p.m., New York City time, on the expiration
date of the exchange offer.
 
    To withdraw a tender of old notes in the exchange offer, a letter or
facsimile transmission notice of withdrawal must be received by the exchange
agent at its address set forth below prior to 5:00 p.m., New York City time, on
the expiration date. Any notice of withdrawal must:
 
    - specify the name of the person having deposited the old notes to be
      withdrawn,
 
    - identify the old notes to be withdrawn including the certificate number(s)
      and principal amount of such old notes or, in the case of old notes
      transferred by book-entry transfer, the name and number of the account at
      the book-entry transfer facility to be credited and otherwise comply with
      the procedures of the transfer agent,
 
    - be signed by the holder in the same manner as the original signature on
      the letter of transmittal by which the old notes were tendered, including
      any required signature guarantees, or be accompanied by documents of
      transfer sufficient to have the trustee under the indenture governing the
      old notes register the transfer of the old notes into the name of the
      person withdrawing the tender, and
 
    - specify the name in which any such old notes are to be registered, if
      different from that of the person who deposited the notes.
 
    If certificates for old notes have been delivered or otherwise identified to
the exchange agent, then, before the release of the certificates, the
withdrawing holder must also submit the serial numbers of the particular
certificates to be withdrawn and a signed notice of withdrawal with signatures
guaranteed by an eligible guarantor institution unless the holder is an eligible
guarantor institution.
 
    All questions as to the validity, form and eligibility, including time of
receipt, of such notices will be determined by NEXTLINK, whose determination
shall be final and binding on all parties. Any old notes so withdrawn will be
deemed not to have been validly tendered for purposes of the exchange offer, and
no new notes will be issued, unless the old notes so withdrawn are validly
retendered. Any old notes which have been tendered but which are not accepted
for exchange will be returned to the holder of the notes without cost to the
holder as soon as practicable after withdrawal, rejection of tender or
termination of the exchange offer. Properly withdrawn old notes may be
retendered by following one of the procedures described above under
"--Procedures for Tendering" at any time before the expiration date.
 
                                       37
<PAGE>
CONDITIONS
 
    Despite any other term of the exchange offer, NEXTLINK shall not be required
to accept for exchange, or exchange new notes for, any old notes and may
terminate the exchange offer as provided in this prospectus before the
acceptance of the old notes, if:
 
    (1) any action or proceeding is instituted or threatened in any court or by
       or before any governmental agency with respect to the exchange offer
       which, in the reasonable judgment of NEXTLINK, might materially impair
       the ability of NEXTLINK to proceed with the exchange offer or materially
       impair the contemplated benefits of the exchange offer to NEXTLINK, or
       any material adverse development has occurred in any existing action or
       proceeding with respect to NEXTLINK or any of its subsidiaries;
 
    (2) any law, statute, rule or regulation is proposed, adopted or enacted,
       which in the reasonable judgment of NEXTLINK, might materially impair the
       ability of NEXTLINK to proceed with the exchange offer or materially
       impair the contemplated benefits of the exchange offer to NEXTLINK; or
 
    (3) any governmental approval has not been obtained, which approval NEXTLINK
       shall, in its reasonable discretion, deem necessary for the consummation
       for the exchange offer as contemplated by this prospectus.
 
    The conditions listed above are for the sole benefit of NEXTLINK and may be
asserted by NEXTLINK regardless of the circumstances giving rise to any of these
conditions. NEXTLINK may waive these conditions in its reasonable discretion in
whole or in part at any time and from time to time. The failure by NEXTLINK at
any time to exercise any of the above rights shall not be deemed a waiver of
such right and such right shall be deemed an ongoing right which may be asserted
at any time and from time to time.
 
    If NEXTLINK determines in its reasonable discretion that any of the
conditions are not satisfied, NEXTLINK may:
 
    (1) refuse to accept any old notes and return all tendered old notes to the
       tendering holders,
 
    (2) extend the exchange offer and retain all old notes tendered before the
       expiration of the exchange offer, subject, however, to the rights of
       holders to withdraw these old notes (See "--Withdrawal of Tenders" above)
       or
 
    (3) waive unsatisfied conditions with respect to the exchange offer and
       accept all properly tendered old notes which have not been withdrawn. If
       this waiver constitutes a material change to the exchange offer, NEXTLINK
       will promptly disclose the waiver by means of a prospectus supplement
       that will be distributed to the registered holders. NEXTLINK will also
       extend the exchange offer for a period of five to ten business days,
       depending upon the significance of the waiver and the manner of
       disclosure to the registered
 
                                       38
<PAGE>
       holders, if the exchange offer would otherwise expire during such five to
       ten business day period.
 
EXCHANGE AGENT
 
    United States Trust Company has been appointed as exchange agent for the
exchange offer. Questions and requests for assistance and requests for
additional copies of this prospectus or of the letter of transmittal should be
directed to United States Trust Company addressed as follows:
 
                         For Information by Telephone:
                                (212) 8952-1664
 
                     By Hand or Overnight Delivery Service:
                          United States Trust Company
                              114 West 47th Street
                            New York, New York 10036
                          Attention: Patricia Stermer,
                             Reorganization Section
                           By Facsimile Transmission:
                                 (212) 852-1625
                            (Telephone Confirmation)
                                 (212) 852-1664
 
    United States Trust Company also acts as trustee under the indenture
governing the notes.
 
FEES AND EXPENSES
 
    NEXTLINK will bear the expenses of soliciting tenders. NEXTLINK has not
retained any dealer-manager in connection with the exchange offer and will not
make any payments to brokers, dealers or others soliciting acceptances of the
exchange offer. NEXTLINK, however, will pay the exchange agent reasonable and
customary fees for its services and will reimburse it for its reasonable
out-of-pocket expenses in connection with providing the services.
 
    The cash expenses to be incurred in connection with the exchange offer will
be paid by NEXTLINK. Such expenses include fees and expenses of United States
Trust Company as exchange agent and as trustee under the indenture governing the
notes, accounting and legal fees and printing costs, among others.
 
ACCOUNTING TREATMENT
 
    The new notes will be recorded at the same carrying value as the old notes
as reflected in NEXTLINK's accounting records on the date of exchange.
Accordingly, no gain or loss for accounting purposes will be recognized by
NEXTLINK. The
 
                                       39
<PAGE>
expenses of the exchange offer and the unamortized expenses related to the
issuance of the old notes will be amortized over the term of the notes.
 
CONSEQUENCES OF FAILURE TO EXCHANGE
 
    Holders of old notes who are eligible to participate in the exchange offer
but who do not tender their old notes will not have any further registration
rights, and their old notes will continue to be subject to restrictions on
transfer. Accordingly, such old notes may be resold only:
 
    - to NEXTLINK, upon redemption of these notes or otherwise,
 
    - so long as the old notes are eligible for resale pursuant to Rule 144A
      under the Securities Act, to a person inside the United States whom the
      seller reasonably believes is a qualified institutional buyer within the
      meaning of Rule 144A in a transaction meeting the requirements of Rule
      144A,
 
    - in accordance with Rule 144 under the Securities Act, or under another
      exemption from the registration requirements of the Securities Act, and
      based upon an opinion of counsel reasonably acceptable to NEXTLINK,
 
    - outside the United States to a foreign person in a transaction meeting the
      requirements of Rule 904 under the Securities Act, or
 
    - under to an effective registration statement under the Securities Act,
 
in each case in accordance with any applicable securities laws of any state of
the United States.
 
REGULATORY APPROVALS
 
    NEXTLINK does not believe that the receipt of any material federal or state
regulatory approval will be necessary in connection with the exchange offer,
other than the effectiveness of the exchange offer registration statement under
the Securities Act.
 
OTHER
 
    Participation in the exchange offer is voluntary and holders of old notes
should carefully consider whether to accept the terms and condition of this
offer. Holders of the old notes are urged to consult their financial and tax
advisors in making their own decisions on what action to take with respect to
the exchange offer.
 
                                       40
<PAGE>
                            DESCRIPTION OF THE NOTES
 
    The new notes, like the old notes, will be issued under the indenture, dated
November 12, 1998, between NEXTLINK and United States Trust Company, as trustee.
The new notes are the same as the old notes except that the new notes
 
    - will not bear legends restricting their transfer and
 
    - will not contain certain terms providing for an increase in the interest
      rate under the circumstances described in the registration rights
      agreement.
 
    The indenture and its associated documents contain the full legal text of
the matters described in this section. A copy of the indenture has been filed
with the commission as part of our Registration Statement. See "Where You Can
Find More Information" on page 18 for information on how to obtain a copy.
 
    Because this section is a summary, it does not describe every aspect of the
notes. This summary is subject to and qualified in its entirety by reference to
all the provisions of the indenture, including definitions of some terms used in
the indenture. For example, in this section we use capitalized words to signify
defined terms that have been given special meaning in the indenture. We describe
the meaning for only the more important terms, under "Definitions". We also
include references in parentheses to certain sections of the indenture. Whenever
we refer to particular sections or defined terms of the indenture in this
prospectus, these sections or defined terms are incorporated by reference into
this prospectus.
 
    In this description of notes, the term "NEXTLINK" refers to NEXTLINK
Communications, Inc. and does not include its subsidiaries except for purposes
of financial data determined on a consolidated basis.
 
BRIEF DESCRIPTION OF THE NOTES
 
    These notes:
 
    - will be senior obligations of NEXTLINK;
 
    - will be limited to $500 million aggregate principal amount;
 
    - will mature on November 15, 2008; and
 
    - will bear interest at the rate of 10 3/4% per annum.
 
    Interest will be paid semi-annually on May 15 and November 15 of each year,
commencing May 15, 1999, to the registered holder at the close of business on
the preceding May 1 or November 1.
 
    Interest on the notes will be computed on the basis of a 360 day year of
twelve 30 day months. (Section 301, 307 and 310)
 
                                       41
<PAGE>
METHODS OF RECEIVING PAYMENTS ON THE NOTES
 
    NEXTLINK will pay interest, principal and any other money due on the notes
at the corporate trust office of the trustee in New York City. That office is
currently located at 114 West 47th Street, New York, New York 10036. You must
make arrangements to have your payments picked up at or wired from that office.
NEXTLINK may also choose to pay interest by mailing checks. (Section301, 305 and
1002)
 
    The notes will be issued only in fully registered form, without coupons, in
denominations of $1,000 and any integral multiple of $1,000. (Section302) You
will not be required to pay a service charge to transfer or exchange notes, but
you may be required to pay for any tax or other governmental charge associated
with the exchange or transfer. (Section305)
 
RANKING
 
    The notes:
 
    - will be senior obligations of NEXTLINK;
 
    - will rank equally in right of payment with all existing and future senior
      obligations of NEXTLINK, including the 9% Notes, the 9 5/8% Notes, the
      12 1/2% Notes and the 9.45% Notes; and
 
    - will rank senior in right of payment to all future subordinated
      obligations of NEXTLINK.
 
    Holders of secured obligations of NEXTLINK will, however, have claims that
are prior to the claims of the holders of the notes with respect to the assets
securing those other obligations.
 
    NEXTLINK's principal operations are conducted through its Subsidiaries, and
NEXTLINK is therefore dependent upon the cash flow of its Subsidiaries to meet
its obligations. NEXTLINK's Subsidiaries will have no obligation to guarantee or
otherwise pay amounts due under the notes. Therefore, the notes will be
effectively subordinated to all indebtedness and other liabilities and
commitments, including trade payables, of NEXTLINK's Subsidiaries. Any right of
NEXTLINK to receive assets of any Subsidiary upon any liquidation or
reorganization of that Subsidiary (and the consequent right of holders of the
notes to participate in those assets) will be effectively subordinated to the
claims of the Subsidiary's creditors, except to the extent that NEXTLINK itself
is recognized as a creditor of the Subsidiary. See "Risk Factors--the notes that
you hold are structurally subordinated to the obligations of our subsidiaries."
 
    As of December 31, 1998:
 
    - the total amount of outstanding consolidated liabilities of NEXTLINK and
      its Subsidiaries, including trade payables, were approximately $2,173.4
      million, of which $15.8 million were secured obligations; and
 
                                       42
<PAGE>
    - the total amount of outstanding liabilities of NEXTLINK's Subsidiaries,
      including trade payables, were $91.9 million, of which $1.5 million were
      secured obligations.
 
    For more information, see "Description of Other Indebtedness" and "Selected
Historical Consolidated Financial and Operating Data."
 
OPTIONAL REDEMPTION
 
    NEXTLINK may opt to redeem the notes, in whole or in part, at any time on or
after November 15, 2003. If NEXTLINK chooses this optional redemption, it is
required to mail a notice of the redemption not less than 30 and not more than
60 days after the redemption to each holder of notes to be redeemed at this
holders address as it appears in the note register
 
<TABLE>
<CAPTION>
YEAR                                                                      REDEMPTION PRICE
- ------------------------------------------------------------------------  ----------------
<S>                                                                       <C>
2003....................................................................        105.375%
2004....................................................................        103.583%
2005....................................................................        101.792%
2006 and thereafter.....................................................        100.000%
</TABLE>
 
    The prices are expressed as percentages of the principal amount.
 
(SectionSection 203, 1101, 1105 and 1107)
 
    NEXTLINK may only redeem the notes in amounts of $1,000 principal amount or
an integral multiple of $1,000 at a redemption price of 112.750% of their
principal amount plus accrued and unpaid interest before November 15, 2003, if,
on or before November 2001, NEXTLINK receives net proceeds from a sale of its
Common Equity.
 
    If, in addition:
 
    - at least 66 2/3% of the original aggregate principal amount of the note
      remains outstanding after the redemption; and
 
    - the redemption occurs on a redemption date within 90 days of the sale and
      NEXTLINK mails not less than 30 and not more than 60 days after the
      redemption a notice to each holder of notes to be redeemed
 
    NEXTLINK may opt to use all or a portion of any such net proceeds to redeem
notes in a principal amount of up to 33 1/2% of the original principal amount of
the notes.
 
    If less than all the notes are to be redeemed, the trustee shall select the
particular notes to be redeemed or any portion thereof that is an integral
multiple of $1,000. The trustee shall make this selection on a pro rata basis,
by lot or by such other method as it shall deem fair and appropriate.
 
                                       43
<PAGE>
MANDATORY REDEMPTION; SINKING FUND
 
    Except as described under "Covenants--Limitation on Asset Dispositions" and
"Covenants--Change of Control" below, NEXTLINK is not required to purchase or
make mandatory redemption payments or sinking fund payments with respect to the
notes.
 
COVENANTS
 
    In the indenture, NEXTLINK agreed to certain restrictions that limit its and
its Restricted Subsidiaries' ability to:
 
       (1) Incur additional Debt;
 
       (2) issue Preferred Stock;
 
       (3) pay dividends, acquire shares of Capital Stock of NEXTLINK, make
              Investments or redeem Debt of NEXTLINK which is subordinate in
              right of payment to the notes;
 
       (4) restrict the ability of any Restricted Subsidiary to pay dividends,
              to make loans or advances to NEXTLINK or any other Restricted
              Subsidiary or to transfer any of its property or assets to
              NEXTLINK or any other Restricted Subsidiary;
 
       (5) create liens;
 
       (6) engage in sale-leaseback transactions;
 
       (7) make Asset Dispositions;
 
       (8) issue or sell shares of Capital Stock of Restricted Subsidiaries; and
 
       (9) enter into transactions with Affiliates and Related Persons.
 
    In addition, if a Change of Control occurs, each holder of notes will have
the right to require NEXTLINK to repurchase all or part of such holder's notes
at a price equal to 101% of their principal amount plus accrued and unpaid
interest to the date of purchase. The above limitations are "restrictive
covenants" that are promises that we make to you about how we will run our
business, or business actions that we promise not to take. A more detailed
description of the restrictive covenants and the exceptions to them follows
below.
 
    LIMITATION ON CONSOLIDATED INDEBTEDNESS
 
    NEXTLINK may not, and may not permit any Restricted Subsidiary to, Incur any
Debt unless either:
 
       (1) the ratio of
 
              (a) the aggregate consolidated principal amount of Debt of
                  NEXTLINK outstanding as of the most recent available quarterly
                  or annual balance sheet, after giving pro forma effect to the
                  Incurrence of such Debt and any other Debt Incurred since such
 
                                       44
<PAGE>
                  balance sheet date and the receipt and application of the
                  proceeds thereof to
 
              (b) Consolidated Cash Flow Available for Fixed Charges for the
                  four full fiscal quarters next preceding the Incurrence of
                  such Debt for which consolidated financial statements are
                  available, determined on a pro forma basis as if
 
              (x) any such Debt had been Incurred and the proceeds thereof had
                  been applied at the beginning of such four fiscal quarters;
 
              (y) the net income (or loss) for such period of any Person or
                  related to any assets disposed of by NEXTLINK or a Restricted
                  Subsidiary prior to the end of such period had been excluded
                  from Consolidated Net Income; and
 
              (z) the net income (or loss) for such period of any Person or
                  related to any assets acquired by NEXTLINK or any Restricted
                  Subsidiary prior to the end of such period had been included
                  in Consolidated Net Income;
 
       would be less than 5.5 to 1 for such four quarter periods ending on or
       prior to December 31, 1999 and 5.0 to 1 for such periods ending
       thereafter; or
 
    (2) NEXTLINK's Consolidated Capital Ratio as of the most recent available
       quarterly or annual balance sheet, after giving pro forma effect to the
       Incurrence of such Debt, any issuance of capital stock (other than
       Disqualified Stock) since such balance sheet date, any increase in
       paid-in-capital (other than in respect of Disqualified Stock) since such
       balance sheet date and the Incurrence of any other Debt since such
       balance sheet date and the receipt and application of the proceeds
       thereof, is less than 2.0 to 1.
 
    Notwithstanding the foregoing limitation, NEXTLINK and any Restricted
Subsidiary may Incur the following:
 
    (1) Debt under any one or more Bank Credit Agreements or Vendor Financing
       Facilities in an aggregate principal amount at any one time not to exceed
       the greater of
 
       (a) $175 million and
 
       (b) 85% of the Eligible Receivables, and any renewal, extension,
              refinancing or refunding thereof in an amount which, together with
              any principal amount remaining outstanding or available under all
              Bank Credit Agreements and Vendor Financing Facilities of NEXTLINK
              and its Restricted Subsidiaries, plus the amount of any premium
              required to be paid in connection with such refinancing pursuant
              to the terms of any Bank Credit Agreement so refinanced plus the
              amount of expenses incurred in connection with such refinancing,
              does not exceed the aggregate principal amount outstanding or
              available under all such Bank
 
                                       45
<PAGE>
              Credit Agreements and Vendor Financing Facilities of NEXTLINK and
              its Restricted Subsidiaries immediately prior to such renewal,
              extension, refinancing or refunding;
 
    (2) Purchase Money Debt Incurred to finance the construction, acquisition or
       improvement of Telecommunications Assets, provided that the net proceeds
       of such Purchase Money Debt do not exceed 100% of the cost of
       construction, acquisition or improvement price of the applicable
       Telecommunications Assets;
 
    (3) Debt owed by NEXTLINK to any Restricted Subsidiary of NEXTLINK or Debt
       owed by a Restricted Subsidiary to NEXTLINK or a Restricted Subsidiary of
       NEXTLINK; provided, however, that upon either
 
       (a) the transfer or other disposition by such Restricted Subsidiary or
              NEXTLINK of any Debt so permitted to a Person other than NEXTLINK
              or another Restricted Subsidiary of NEXTLINK or
 
       (b) the issuance (other than directors' qualifying shares), sale, lease,
              transfer or other disposition of shares of Capital Stock
              (including by consolidation or merger) of such Restricted
              Subsidiary, as a result of which the obligor of such Debt ceases
              to be a Restricted Subsidiary, the provisions of this clause (3)
              shall no longer be applicable to such Debt and such Debt shall be
              deemed to have been Incurred at the time of such transfer or other
              disposition;
 
    (4) Debt Incurred to renew, extend, refinance or refund (each, a
       "refinancing") Debt outstanding at the date of the indenture or incurred
       pursuant to the preceding paragraph or clause (2) of this paragraph or
       the notes in an aggregate principal amount not to exceed the aggregate
       principal amount of and accrued interest on the Debt so refinanced plus
       the amount of any premium required to be paid in connection with such
       refinancing pursuant to the terms of the Debt so refinanced or the amount
       of any premium reasonably determined by NEXTLINK as necessary to
       accomplish such refinancing by means of a tender offer or privately
       negotiated repurchase, plus the amount of expenses of NEXTLINK incurred
       in connection with such refinancing; provided, however, that Debt the
       proceeds of which are used to refinance the notes or Debt which is pari
       passu to the notes or debt which is subordinate in right of payment to
       the notes shall only be permitted if
 
       (a) in the case of any refinancing of the notes or Debt which is pari
              passu to the notes, the refinancing Debt is made pari passu to the
              notes or subordinated to the notes, and, in the case of any
              refinancing of Debt which is subordinated to the notes, the
              refinancing Debt constitutes Subordinated Debt and
 
       (b) in either case, the refinancing Debt by its terms, or by the terms of
              any agreement or instrument pursuant to which such Debt is issued,
 
                                       46
<PAGE>
              (x) does not provide for payments of principal of such Debt at the
                  stated maturity thereof or by way of a sinking fund applicable
                  thereto or by way of any mandatory redemption, defeasance,
                  retirement or repurchase thereof by NEXTLINK (including any
                  redemption, retirement or repurchase which is contingent upon
                  events or circumstances, but excluding any retirement required
                  by virtue of acceleration of such Debt upon any event of
                  default thereunder), in each case prior to the time the same
                  are required by the terms of the Debt being refinanced and
 
              (y) does not permit redemption or other retirement (including
                  pursuant to an offer to purchase made by NEXTLINK) of such
                  debt at the option of the holder thereof prior to the final
                  stated maturity of the Debt being refinanced, other than a
                  redemption or other retirement at the option of the holder of
                  such Debt (including pursuant to an offer to purchase made by
                  NEXTLINK) which is conditioned upon a change substantially
                  similar to those described under "--Change of Control" or
                  which is pursuant to provisions substantially similar to those
                  described under "--Limitation on Asset Dispositions".
 
    (5) Debt consisting of Permitted Interest Rate or Currency Protection
       Agreements;
 
    (6) Debt outstanding under the notes;
 
    (7) Subordinated Debt invested by
 
       (a) a group of employees of NEXTLINK, which includes the Chief Executive
              Officer of NEXTLINK, who own, directly or indirectly, through an
              employee stock ownership plan or arrangement, shares of NEXTLINK's
              Capital Stock or
 
       (b) any other Person that controls NEXTLINK
 
              (x) on the Issue Date or
 
              (y) after a Change of Control, provided that NEXTLINK is not in
                  default with respect to its obligations described under
                  "--Change of Control" below;
 
    (8) Debt consisting of performance and other similar bonds and reimbursement
       obligations Incurred in the ordinary course of business securing the
       performance of contractual, franchise or license obligations of NEXTLINK
       or a Restricted Subsidiary, or in respect of a letter of credit obtained
       to secure such performance; and
 
    (9) Debt not otherwise permitted to be Incurred pursuant to clauses (1)
       through (8) above, which, together with any other outstanding Debt
       Incurred pursuant to this clause (9), has an aggregate principal amount
       or, in the case of Debt issued at a discount, an accreted amount
       (determined in accordance
 
                                       47
<PAGE>
       with generally accepted accounting principles) at the time of Incurrence
       not in excess of $10 million at any time outstanding.
 
    For purposes of determining compliance with this "Limitation on Consolidated
Debt" covenant, if an item of Debt meets the criteria of more than one of the
types of Debt NEXTLINK is permitted to incur pursuant to the foregoing clauses
(1) through (9) or the first unnumbered paragraph of this "Limitation on
Consolidated Indebtedness," NEXTLINK shall have the right, in its sole
discretion, to classify such item of Debt and shall only be required to include
the amount and type of such Debt under the clause or paragraph permitting the
Debt as so classified. For purposes of determining any particular amount of Debt
under such covenant, Guarantees or Liens with respect to letters of credit
supporting Debt otherwise included in the determination of a particular amount
shall not be included. (Section 1007)
 
    LIMITATION ON DEBT AND PREFERRED STOCK OF RESTRICTED SUBSIDIARIES
 
    NEXTLINK may not permit any Restricted Subsidiary (other than a Restricted
Subsidiary that has fully and unconditionally Guaranteed the notes on an
unsubordinated basis) to Incur or suffer to exist any Debt or issue any
Preferred Stock except:
 
    (1) Debt or Preferred Stock outstanding on the date of the Indenture after
       giving effect to the application of the proceeds of the notes;
 
    (2) Debt Incurred or Preferred Stock issued to and held by NEXTLINK or a
       Restricted Subsidiary of NEXTLINK (provided that such Debt or Preferred
       Stock is at all times held by NEXTLINK or a Restricted Subsidiary of
       NEXTLINK);
 
    (3) Debt Incurred or Preferred Stock issued by a Person prior to the time
 
       (a) such Person became a Restricted Subsidiary of NEXTLINK,
 
       (b) such Person merges into or consolidates with a Restricted Subsidiary
              of NEXTLINK or
 
       (c) another Restricted Subsidiary of NEXTLINK merges into or consolidates
              with such Person (in a transaction in which such Person becomes a
              Restricted Subsidiary of NEXTLINK), which Debt or Preferred Stock
              was not Incurred or issued in anticipation of such transaction and
              was outstanding prior to such transaction;
 
    (4) Debt consisting of Permitted Interest Rate and Currency Protection
       Agreements;
 
    (5) Debt or Preferred Stock of a Joint Venture;
 
    (6) Debt under any one or more Bank Credit Agreements or Vendor Financing
       Facilities (and renewals, extensions, refinancings or refundings thereof)
       which is permitted to be outstanding under clause (1) of the
       "--Limitation on Consolidated Indebtedness";
 
                                       48
<PAGE>
    (7) Debt consisting of Guarantees of the Notes;
 
    (8) Debt or Preferred Stock which is exchanged for, or the proceeds of which
       are used to refinance, refund or redeem, any Debt or Preferred Stock
       permitted to be outstanding pursuant to clauses (1), (3) and (9) hereof
       (or any extension or renewal thereof) (for purposes hereof, a
       "refinancing"), in an aggregate principal amount, in the case of Debt, or
       with an aggregate liquidation preference, in the case of Preferred Stock,
       not to exceed the aggregate principal amount of the Debt so refinanced or
       the aggregate liquidation preference of the Preferred Stock so
       refinanced, plus the amount of any premium required to be paid in
       connection with such refinancing pursuant to the terms of the Debt or
       Preferred Stock so refinanced or the amount of any premium reasonably
       determined by NEXTLINK as necessary to accomplish such refinancing by
       means of a tender offer or privately negotiated repurchase, plus the
       amount of expenses of NEXTLINK and the Restricted Subsidiary incurred in
       connection therewith and provided the Debt or Preferred Stock incurred or
       issued upon such refinancing by its terms, or by the terms of any
       agreement or instrument pursuant to which such Debt or Preferred Stock is
       Incurred or issued,
 
       (a) does not provide for payments of principal or liquidation value at
              the stated maturity of such Debt or Preferred Stock or by way of a
              sinking fund applicable to such Debt or Preferred Stock or by way
              of any mandatory redemption, defeasance, retirement or repurchase
              of such Debt or Preferred Stock by NEXTLINK or any Restricted
              Subsidiary of NEXTLINK (including any redemption, retirement or
              repurchase which is contingent upon events or circumstances, but
              excluding any retirement required by virtue of acceleration of
              such Debt upon an event of default thereunder), in each case prior
              to the time the same are required by the terms of the Debt or
              Preferred Stock being refinanced and
 
       (b) does not permit redemption or other retirement (including pursuant to
              an offer to purchase made by NEXTLINK or a Restricted Subsidiary)
              of such Debt or Preferred Stock at the option of the holder
              thereof prior to the stated maturity of the Debt or Preferred
              Stock being refinanced, other than a redemption or other
              retirement at the option of the holder of such Debt or Preferred
              Stock (including pursuant to an offer to purchase made by NEXTLINK
              or a Restricted Subsidiary) which is conditioned upon the change
              of control of NEXTLINK pursuant to provisions substantially
              similar to those contained in the Indenture described under
              "--Change of Control" or which is pursuant to provisions
              substantially similar to those described under "--Limitation on
              Asset Dispositions", and provided, further, that in the case of
              any exchange or redemption of Preferred Stock of a Restricted
              Subsidiary, such Preferred Stock may only be exchanged for or
              redeemed with Preferred Stock of such Restricted Subsidiary;
 
                                       49
<PAGE>
    (9) Purchase Money Debt Incurred to finance the construction, acquisition or
       improvement of Telecommunications Assets, provided that the net proceeds
       of such Purchase Money Debt do not exceed 100% of the cost of
       construction, acquisition or improvement price of the applicable
       Telecommunications Assets;
 
    (10) Debt consisting of performance and other similar bonds and
       reimbursement obligations Incurred in the ordinary course of business
       securing the performance of contractual, franchise or license obligations
       of NEXTLINK or a Restricted Subsidiary, or in respect of a letter of
       credit obtained to secure such performance; and
 
    (11) Debt not otherwise permitted to be incurred pursuant to clauses (1)
       through (10) above, which, together with any other outstanding Debt
       incurred pursuant to this clause (11), has an aggregate principal amount
       (or, in the case of Debt issued at a discount, an accreted amount
       (determined in accordance with generally accepted accounting principles)
       at the time of Incurrence) not in excess of $10 million at any time
       outstanding. (Section 1008)
 
    For purposes of determining compliance with this "Limitation on Debt and
Preferred Stock of Restricted Subsidiaries" covenant, in the event that an item
of Debt meets the criteria of more than one of the types of Debt a Restricted
Subsidiary is permitted to incur pursuant to the foregoing clauses (1) through
(9), NEXTLINK shall have the right, in its sole discretion, to classify such
item of Debt and shall be only required to include the amount and type of such
Debt under the clause permitting the Debt as so classified. For purposes of
determining any particular amount of Debt under such covenant, Guarantees or
Liens with respect to letters of credit supporting Debt or otherwise included in
the determination of a particular amount shall not be included.
 
LIMITATION ON RESTRICTED PAYMENTS
 
    NEXTLINK may not:
 
    (1) directly or indirectly, declare or pay any dividend, or make any
       distribution, in respect of its Capital Stock or to the holders thereof
       (in their capacity as such), excluding any dividends or distributions
       payable solely in shares of its Capital Stock (other than Disqualified
       Stock) or in options, warrants or other rights to acquire its Capital
       Stock (other than Disqualified Stock);
 
    (2) and may not permit any Restricted Subsidiary to, purchase, redeem, or
       otherwise retire or acquire for value
 
       (a) any Capital Stock of NEXTLINK or any Related Person of NEXTLINK; or
 
       (b) any options, warrants or rights to purchase or acquire shares of
              Capital Stock of NEXTLINK or any Related Person of NEXTLINK or any
              securities convertible or exchangeable into shares of Capital
              Stock of NEXTLINK or any Related Person of NEXTLINK;
 
                                       50
<PAGE>
    (3) make, or permit any Restricted Subsidiary to make, any Investment in, or
       payment on a Guarantee of any obligation of, any Person, other than
       NEXTLINK or a Restricted Subsidiary of NEXTLINK, except for Permitted
       Investments; and
 
    (4) and may not permit any Restricted Subsidiary to, redeem, defease,
       repurchase, retire or otherwise acquire or retire for value, prior to any
       scheduled maturity, repayment or sinking fund payment, Debt of NEXTLINK
       which is subordinate in right of payment to the Notes (each of clauses
       (1) through (4) being a "Restricted Payment")
 
        if:
 
       (a) a Default or an Event of Default shall have occurred and is
              continuing; or
 
       (b) upon giving effect to such Restricted Payment, NEXTLINK could not
              Incur at least $1.00 of additional Debt pursuant to the terms of
              the Indenture described in the first paragraph of "--Limitation on
              Consolidated Indebtedness" above; or
 
       (c) upon giving effect to such Restricted Payment, the aggregate of all
              Restricted Payments from April 25, 1996 exceeds the sum of:
 
              (A) 50% of cumulative Consolidated Net Income (or, in the case
                  Consolidated Net Income shall be negative, less 100% of such
                  deficit) since the end of the last full fiscal quarter prior
                  to April 25, 1996 through the last day of the last full fiscal
                  quarter ending immediately preceding the date of such
                  Restricted Payment; plus
 
              (B) $5 million; plus
 
              (C) 100% of the net reduction in Investments in any Unrestricted
                  Subsidiary resulting from payments of interest on Debt,
                  dividends, repayments of loans or advances, or other transfers
                  of assets, in each case to NEXTLINK or any Restricted
                  Subsidiary of NEXTLINK from such Unrestricted Subsidiary
                  (except to the extent that any such payment is included in the
                  calculation of Consolidated Net Income) or from redesignations
                  of Unrestricted Subsidiaries as Restricted Subsidiaries;
                  PROVIDED that the amount included in this clause (C) shall not
                  exceed the amount of Investments previously made by NEXTLINK
                  and its Restricted Subsidiaries in such Unrestricted
                  Subsidiary;
 
       PROVIDED, FURTHER, that NEXTLINK or a Restricted Subsidiary of NEXTLINK
       may make any Restricted Payment with the aggregate net proceeds received
       after April 25, 1996, including the fair value of property other than
       cash (determined in good faith by the Board of Directors of NEXTLINK, as
       conclusively evidenced by a Board Resolution filed with the trustee), as
       capital contributions to NEXTLINK or from the issuance (other than to a
 
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       Restricted Subsidiary) of Capital Stock (other than Disqualified Stock)
       of NEXTLINK and warrants, rights or options on Capital Stock (other than
       Disqualified Stock) of NEXTLINK and the principal amount of Debt of
       NEXTLINK that has been converted into Capital Stock (other than
       Disqualified Stock and other than by a Restricted Subsidiary) of NEXTLINK
       after April 25, 1996.
 
    Notwithstanding the foregoing:
 
    (1) NEXTLINK may pay any dividend on Capital Stock of any class within 60
       days after the declaration thereof if, on the date when the dividend was
       declared, NEXTLINK could have paid such dividend in accordance with the
       foregoing provisions
 
    (2) NEXTLINK may repurchase any shares of its Common Equity or options to
       acquire its Common Equity from Persons who were formerly officers or
       employees of NEXTLINK, PROVIDED that the aggregate amount of all such
       repurchases made pursuant to this clause (2) shall not exceed $2 million,
       plus the aggregate cash proceeds received by NEXTLINK since April 25,
       1996 from issuances of its Common Equity or options to acquire its Common
       Equity to members, officers, managers, directors and employees of
       NEXTLINK or any of its Subsidiaries;
 
    (3) NEXTLINK and its Restricted Subsidiaries may refinance any Debt
       otherwise permitted by clause (4) of the second paragraph under
       "--Limitation on Consolidated Indebtedness" above; and
 
    (4) NEXTLINK and its Restricted Subsidiaries may retire or repurchase any
       Capital Stock or Subordinated Debt of NEXTLINK in exchange for, or out of
       the proceeds of the substantially concurrent sale (other than to a
       Restricted Subsidiary of NEXTLINK) of, Capital Stock (other than
       Disqualified Stock) of NEXTLINK. If NEXTLINK makes a Restricted Payment
       which, at the time it is made, would in good faith determination of
       NEXTLINK be permitted under the Indenture, such Restricted Payment shall
       be deemed to have been made in compliance with the Indenture
       notwithstanding any subsequent adjustments in good faith to NEXTLINK
       financial statements affecting Consolidated Net Income for any period.
 
    In determining the aggregate amount expended or available for Restricted
Payments in accordance with clause (c) of the first paragraph above,
 
    (1) no amounts expended under clauses (3) or (4) of the immediately
       preceding paragraph shall be included,
 
    (2) 100% of the amounts expended under clauses (1) and (2) of the
       immediately preceding paragraph shall be included, and
 
    (3) no amount shall be credited in respect of issuances of Capital Stock in
       transactions under clause (4) of the immediately preceding paragraph.
       (Section 1009)
 
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<PAGE>
LIMITATION ON DIVIDEND AND OTHER PAYMENT RESTRICTIONS AFFECTING RESTRICTED
  SUBSIDIARIES
 
    NEXTLINK may not, and may not permit any Restricted Subsidiary to, directly
or indirectly, create or otherwise cause or suffer to exist or become effective
any consensual encumbrance or restriction on the ability of any Restricted
Subsidiary of NEXTLINK:
 
    (1) to pay dividends (in cash or otherwise) or make any other distributions
       in respect of its Capital Stock owned by NEXTLINK or any other Restricted
       Subsidiary or pay any Debt or other obligation owed to NEXTLINK or any
       other Restricted Subsidiary;
 
    (2) to make loans or advances to NEXTLINK or any other Restricted
       Subsidiary; or
 
    (3) to transfer any of its property or assets to NEXTLINK or any other
       Restricted Subsidiary.
 
    Notwithstanding the foregoing, NEXTLINK may, and may permit any Restricted
Subsidiary to, suffer to exist any such encumbrance or restriction:
 
       (a) pursuant to any agreement in effect on the Issue Date;
 
       (b) pursuant to an agreement relating to any Acquired Debt, which
              encumbrance or restriction is not applicable to any Person, or the
              properties or assets of any Person, other than the Person so
              acquired and its Subsidiaries;
 
       (c) pursuant to any one or more Bank Credit Agreements or Vendor
              Financing Facilities (and renewals, extensions, refinancings or
              refundings thereof) which is permitted to be outstanding under
              clause (1) of the "Limitation on Consolidated Indebtedness",
              PROVIDED that such restriction is consistent with, and not
              materially more restrictive (as conclusively determined in good
              faith by the Chief Financial Officer of NEXTLINK), taken as a
              whole, than, comparable provisions included in similar agreements
              or facilities extended to comparable credits engaged in the
              Telecommunications Business;
 
       (d) pursuant to an agreement effecting a renewal, refunding or extension
              of Debt Incurred pursuant to an agreement referred to in clause
              (a) or (b) above or (e) below, PROVIDED, HOWEVER, that the
              provisions contained in such renewal, refunding or extension
              agreement relating to such encumbrance or restriction are not
              materially more restrictive (as conclusively determined in good
              faith by the Chief Financial Officer of NEXTLINK), taken as a
              whole, than the provisions contained in the agreement the subject
              thereof;
 
       (e) in the case of clause (3) above, restrictions contained in any
              security agreement (including a Capital Lease Obligation) securing
              Debt of NEXTLINK or a Restricted Subsidiary otherwise permitted
              under the
 
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<PAGE>
              Indenture, but only to the extent such restrictions restrict the
              transfer of the property subject to such security agreement;
 
       (f) in the case of clause (3) above, customary nonassignment provisions
              entered into in the ordinary course of business in leases and
              other agreements;
 
       (g) any restriction with respect to a Restricted Subsidiary of NEXTLINK
              imposed pursuant to an agreement which has been entered into for
              the sale or disposition of all or substantially all of the Capital
              Stock or assets of such Restricted Subsidiary, PROVIDED that
              consummation of such transaction would not result in a Default or
              an Event of Default, that such restriction terminates if such
              transaction is not consummated and that such consummation or
              abandonment of such transaction occurs within one year of the date
              such agreement was entered into;
 
       (h) pursuant to applicable law or regulations;
 
       (i)  pursuant to the indenture and the notes; or
 
       (j)  any restriction on the sale or other disposition of assets or
              property securing Debt as a result of a Permitted Lien on such
              assets or property. (Section 1010)
 
LIMITATION ON LIENS
 
    NEXTLINK may not, and may not permit any Restricted Subsidiary to, Incur or
suffer to exist any Lien on or with respect to any property or assets now owned
or hereafter acquired to secure any Debt without making, or causing such
Restricted Subsidiary to make, effective provision for securing the Notes
 
    (1) equally and ratably with (or prior to) such Debt as to such property for
       so long as such Debt will be so secured or
 
    (2) in the event such Debt is Debt of NEXTLINK which is subordinate in right
       of payment to the Notes, prior to such Debt as to such property for so
       long as such Debt will be so secured.
 
    The foregoing restrictions shall not apply to:
 
    (1) Liens existing on the Issue Date and securing Debt outstanding on the
       Issue Date or securing the Notes or Liens securing Debt incurred pursuant
       to any Bank Credit Agreement or Vendor Financing Facility (whether or not
       such Bank Credit Agreement or Vendor Financing Facility was outstanding
       on the Issue Date);
 
    (2) Liens securing Debt in an amount which, together with the aggregate
       amount of Debt then outstanding or available under the Bank Credit
       Agreement and the Vendor Financing Facility (or under refinancings or
       amendments of such agreements), does not exceed 1.5 times NEXTLINK's
       Consolidated Cash Flow Available for Fixed Charges for the four full
       fiscal quarters preceding the Incurrence of such Lien for which
       consolidated
 
                                       54
<PAGE>
       financial statements are available, determined on a pro forma basis as if
       such Debt had been Incurred and the proceeds thereof had been applied at
       the beginning of such four fiscal quarters;
 
    (3) Liens in favor of NEXTLINK or any Wholly Owned Restricted Subsidiary of
       NEXTLINK;
 
    (4) Liens on real or personal property of NEXTLINK or a Restricted
       Subsidiary of NEXTLINK acquired, constructed or constituting improvements
       made after the Issue Date to secure Purchase Money Debt which is Incurred
       for the construction, acquisition and improvement of Telecommunications
       Assets and is otherwise permitted under the indenture, PROVIDED, HOWEVER,
       that
 
       (a) the net proceeds of any Debt secured by such a Lien does not exceed
              100% of such purchase price or cost of construction or improvement
              of the property subject to such Lien;
 
       (b) such Lien attaches to such property prior to, at the time of or
              within 180 days after the acquisition, completion of construction
              or commencement of operation of such property; and
 
       (c) such Lien does not extend to or cover any property other than the
              property (or identifiable portions thereof) acquired, constructed
              or constituting improvements made with the proceeds of such
              Purchase Money Debt (it being understood and agreed that all Debt
              owed to any single lender or group of lenders or outstanding under
              any single credit facility shall be considered a single Purchase
              Money Debt, whether drawn at one time or from time to time);
 
    (5) Liens to secure Acquired Debt, provided, however, that
 
       (a) such Lien attaches to the acquired asset prior to the time of the
              acquisition of such asset and
 
       (b) such Lien does not extend to or cover any other asset;
 
    (6) Liens to secure Debt Incurred to extend, renew, refinance or refund (or
       successive extensions, renewals, refinancings or refundings), in whole or
       in part, Debt secured by any Lien referred to in the foregoing clauses
       (1), (2), (4) and (5) so long as such Lien does not extend to any other
       property and the principal amount of Debt so secured is not increased
       except as otherwise permitted under clause (4) of "--Limitation on
       Consolidated Indebtedness";
 
    (7) Liens securing Debt not otherwise permitted by the foregoing clauses (1)
       through (4) in an amount not to exceed 5% of NEXTLINK's Consolidated
       Tangible Assets determined as of the most recent available quarterly or
       annual balance sheet; and
 
    (8) Permitted Liens. (Section 1011)
 
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<PAGE>
LIMITATION ON SALE AND LEASEBACK TRANSACTIONS
 
    NEXTLINK may not, and may not permit any Restricted Subsidiary to, enter
into any Sale and Leaseback Transaction unless:
 
    (1) NEXTLINK or such Restricted Subsidiary would be entitled to incur a Lien
       to secure Debt by reason of the provisions described under "--Limitation
       on Liens" above, equal in amount to the Attributable Value of the Sale
       and Leaseback Transaction without equally and ratably securing the notes;
       or
 
    (2) the Sale and Leaseback Transaction is treated as an Asset Disposition
       and all of the conditions of the Indenture described under "--Limitation
       on Asset Dispositions" (including the provisions concerning the
       application of Net Available Proceeds) are satisfied with respect to such
       Sale and Leaseback Transaction, treating all of the consideration
       received in such Sale and Leaseback Transaction in the same manner as
       consideration received in respect of an Asset Disposition for purposes of
       such covenant. (Section 1012)
 
LIMITATION ON ASSET DISPOSITIONS
 
    NEXTLINK may not, and may not permit any Restricted Subsidiary to, make any
Asset Disposition in one or more related transactions occurring within any 12
month period unless:
 
    (1) NEXTLINK or the Restricted Subsidiary, as the case may be, receives
       consideration for such disposition at least equal to the fair market
       value for the assets sold or disposed of as determined by the Board of
       Directors of NEXTLINK in good faith and evidenced by a Board Resolution
       filed with the Trustee, which determination shall be conclusive;
 
    (2) at least 75% of the consideration for such disposition consists of
 
       (a) cash or readily marketable cash equivalents or the assumption of Debt
              of NEXTLINK (other than Debt that is subordinated to the Notes) or
              of the Restricted Subsidiary and release from all liability on the
              Debt assumed;
 
       (b) Telecommunications Assets; or
 
       (c) shares of publicly traded Voting Stock of any Person engaged in the
              Telecommunications Business in the United States; and
 
    (3) all Net Available Proceeds, less any amounts invested in
       Telecommunications Assets (within 180 days prior to and 360 days
       following such disposition), are applied within 360 days of such
       disposition
 
       (a) first, to the permanent repayment or reduction of Debt then
              outstanding under any Bank Credit Agreement or Vendor Financing
              Facility, to the extent such agreements would require such
              application or prohibit payments pursuant to clause (b) following,
 
                                       56
<PAGE>
       (b) second, to the extent of remaining Net Available Proceeds, to make an
              Offer to Purchase outstanding notes at 100% of their principal
              amount, plus accrued interest to the date of purchase, and, to the
              extent required by the terms thereof, any other Debt of NEXTLINK
              that is PARI PASSU with the notes at a price no greater than 100%
              of the principal amount thereof plus accrued interest to the date
              of purchase (or 100% of the accreted value thereof in the case of
              Debt issued at an original issue discount) and
 
       (c) third, to the extent of any remaining Net Available Proceeds
              following the completion of the Offer to Purchase, to the
              repayment of other Debt of NEXTLINK or Debt of a Restricted
              Subsidiary of NEXTLINK, to the extent permitted under the terms
              thereof. To the extent any Net Available Proceeds remain after
              such uses, NEXTLINK and its Restricted Subsidiaries may use such
              amounts for any purposes not prohibited by the indenture. (Section
              1013)
 
    Notwithstanding the foregoing, these provisions shall not apply to any Asset
Disposition which constitutes a transfer, conveyance, sale, lease or other
disposition of all or substantially all of NEXTLINK's properties or assets as
described under "--Mergers, Consolidations and Certain Sales of Assets."
 
LIMITATION ON ISSUANCES AND SALES OF CAPITAL STOCK OF RESTRICTED SUBSIDIARIES
 
    NEXTLINK may not, and may not permit any Restricted Subsidiary to, issue,
transfer, convey, sell or otherwise dispose of any shares of Capital Stock of a
Restricted Subsidiary of NEXTLINK or securities convertible or exchangeable
into, or options, warrants, rights or any other interest with respect to,
Capital Stock of a Restricted Subsidiary of NEXTLINK to any person other than
NEXTLINK or a Wholly Owned Restricted Subsidiary of NEXTLINK except:
 
    (1) in a transaction consisting of a sale of Capital Stock of such
       Restricted Subsidiary owned by NEXTLINK or any Restricted Subsidiary of
       NEXTLINK and that complies with the provisions described under
       "--Limitation on Asset Dispositions" above to the extent such provisions
       apply;
 
    (2) if required, the issuance, transfer, conveyance, sale or other
       disposition of directors' qualifying shares;
 
    (3) in a transaction in which, or in connection with which, NEXTLINK or a
       Restricted Subsidiary acquires at the same time sufficient Capital Stock
       of such Restricted Subsidiary to at least maintain the same percentage
       ownership interest it had prior to such transaction;
 
    (4) constituting the issuance of Preferred Stock permitted by the provisions
       described under "--Limitation on Debt and Preferred Stock of Restricted
       Subsidiaries" above; and
 
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<PAGE>
    (5) Disqualified Stock issued in exchange for, or upon conversion of, or the
       proceeds of the issuance of which are used to redeem, refinance, replace
       or refund shares of Disqualified Stock of such Restricted Subsidiary,
       provided that the amounts of the redemption obligations of such
       Disqualified Stock shall not exceed the amounts of the redemption
       obligations of, and such Disqualified Stock shall have redemption
       obligations no earlier than those required by, the Disqualified Stock
       being exchanged, converted, redeemed, refinanced, replaced or refunded.
       (Section 1014)
 
TRANSACTIONS WITH AFFILIATES AND RELATED PERSONS
 
    NEXTLINK may not, and may not permit any Restricted Subsidiary to, enter
into any transaction (or series of related transactions) with an Affiliate or
Related Person of NEXTLINK (other than NEXTLINK or a Wholly Owned Restricted
Subsidiary of NEXTLINK), including any Investment, but excluding transactions
pursuant to employee compensation arrangements approved by the Board of
Directors of NEXTLINK, either directly or indirectly, unless such transaction is
on terms no less favorable to NEXTLINK or such Restricted Subsidiary than those
that could reasonably be obtained in a comparable arm's length transaction with
an entity that is not an Affiliate or Related Person and is in the best
interests of NEXTLINK or such Restricted Subsidiary. For any transaction that
involves in excess of $1 million but less than or equal to $15 million, the
Chief Executive Officer of NEXTLINK shall determine that the transaction
satisfies the above criteria and shall evidence such a determination by a
certificate filed with the trustee. For any transaction that involves in excess
of $15 million, NEXTLINK shall also obtain an opinion from a nationally
recognized expert with experience in appraising the terms and conditions, taken
as a whole, of the type of transaction (or series of related transactions) for
which the opinion is required stating that such transaction (or series of
related transactions) is on terms and conditions, taken as a whole, no less
favorable to NEXTLINK or such Restricted Subsidiary than those that could be
obtained in a comparable arm's length transaction with an entity that is not an
Affiliate or Related Person of NEXTLINK, which opinion shall be filed with the
Trustee. This covenant shall not apply to Investments by an Affiliate or a
Related Person of NEXTLINK in the Capital Stock (other than Disqualified Stock)
of NEXTLINK or any Restricted Subsidiary of NEXTLINK. (Section 1015)
 
CHANGE OF CONTROL
 
    Within 30 days of the occurrence of a Change of Control, NEXTLINK will be
required to make an Offer Purchase all outstanding Notes at a purchase price
equal to 101% of their principal amount plus accrued and unpaid interest to the
date of purchase. A "Change of Control" will be deemed to have occurred at such
time as either:
 
    (1) any Person or any Persons acting together that would constitute a
       "group" (a "Group") for purposes of Section 13(d) of the Securities
       Exchange Act of
 
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<PAGE>
       1934, or any successor provision thereto (other than Eagle River, Mr.
       Craig O. McCaw and their respective Affiliates or an underwriter engaged
       in a firm commitment underwriting on behalf of NEXTLINK), shall
       beneficially own (within the meaning of Rule 13d-3 under the Exchange
       Act, or any successor provision thereto) more than 50% of the aggregate
       voting power of all classes of Voting Stock of NEXTLINK; or
 
    (2) neither Mr. Craig O. McCaw nor any person designated by him to NEXTLINK
       as acting on his behalf shall be a director of NEXTLINK; or
 
    (3) during any period of two consecutive years, individuals who at the
       beginning of such period constituted the Board of Directors of NEXTLINK
       (together with any new directors whose election by the Board of Directors
       of NEXTLINK or whose nomination for election by the shareholders was
       proposed by a vote of a majority of the directors of NEXTLINK then still
       in office who were either directors at the beginning of such period or
       whose election or nomination for election was previously so approved)
       cease for any reason to constitute a majority of the Board of Directors
       of NEXTLINK then in office. (Section 1016)
 
    Except as described above with respect to a Change of Control, the indenture
does not contain provisions that permit the holders of the notes to require that
NEXTLINK repurchase or redeem the notes in the event of a takeover,
recapitalization or similar restructuring.
 
    Restrictions in the indenture described herein on the ability of NEXTLINK
and its Restricted Subsidiaries to incur additional Indebtedness, to grant Liens
on its or their property, to make Restricted Payments and to make Asset Sales
may also make more difficult or discourage a takeover of NEXTLINK, whether
favored or opposed by the management of NEXTLINK. Consummation of any such
transaction in certain circumstances may require redemption or repurchase of the
notes, and there can be no assurance that NEXTLINK or the acquiring party will
have sufficient financial resources to effect such redemption or repurchase.
Such restrictions and the restrictions on transactions with Affiliates may, in
certain circumstances, make more difficult or discourage any leveraged buyout of
NEXTLINK or any of its Subsidiaries by the management of NEXTLINK or other
Persons. While such restrictions cover a variety of arrangements which have
traditionally been used to effect highly leveraged transactions, the indenture
may not afford the holders of notes protection in all circumstances from the
adverse aspects of a highly leveraged transaction, reorganization,
restructuring, merger or similar transaction.
 
    In the event of a Change of Control, the indentures relating to the 9.45%
Notes, the 9% Notes, the 9 5/8% Notes and the 12 1/2% Notes would require
NEXTLINK to make an offer to purchase those securities. NEXTLINK does not
currently have adequate financial resources to effect such repurchases and
repurchase the notes upon a Change of Control and there can be no assurance that
NEXTLINK will have such
 
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<PAGE>
resources in the future. The inability of NEXTLINK to repurchase the notes upon
a Change of Control would constitute an Event of Default.
 
    In addition, there may be restrictions contained in instruments evidencing
Indebtedness incurred by NEXTLINK or its Restricted Subsidiaries permitted under
the indenture which restrict or prohibit the ability of NEXTLINK to effect any
repurchase required under the indenture in connection with a Change of Control.
 
    In the event that NEXTLINK makes an Offer to Purchase the notes, NEXTLINK
intends to comply with any applicable securities laws and regulations, including
any applicable requirements of Section 14(e) of, and Rule 14e-1 under, the
Exchange Act.
 
PROVISION OF FINANCIAL INFORMATION
 
    NEXTLINK has agreed that, for so long as any notes remain outstanding, it
will file with the trustee within 15 days after it files them with the
commission copies of the annual and quarterly reports and the information,
documents, and other reports that NEXTLINK is required to file with the
commission pursuant to Section 13(a) or 15(d) of the Exchange Act ("SEC
Reports"). In the event NEXTLINK shall cease to be required to file SEC Reports
pursuant to the Exchange Act, NEXTLINK will nevertheless continue to file such
reports with the commission (unless the commission will not accept such a
filing) and the trustee. NEXTLINK will furnish copies of the SEC Reports to the
holders of notes at the time NEXTLINK is required to file the same with the
trustee and will make such information available to investors who request it in
writing. (Section 1017)
 
LIMITATION ON USE OF PROCEEDS
 
    NEXTLINK will apply the net proceeds from the sale of the old notes toward
the construction, improvement and acquisition by NEXTLINK or one or more
Restricted Subsidiaries of NEXTLINK or Joint Ventures of Telecommunications
Assets of NEXTLINK, such Restricted Subsidiaries or Joint Ventures (or will
advance such net proceeds to such Restricted Subsidiaries of NEXTLINK or Joint
Ventures for such purpose); provided, however, pending such application, the net
proceeds of the sale of the old notes may be invested in Marketable Securities.
(Section 1020)
 
MERGERS, CONSOLIDATIONS AND CERTAIN SALES OF ASSETS
 
    NEXTLINK may not, in a single transaction or a series of related
transactions:
 
    (1) consolidate with or merge into any other Person or permit any other
       Person to consolidate with or merge into NEXTLINK (other than a
       consolidation or merger of a Wholly Owned Restricted Subsidiary organized
       under the laws of a State of the United States into NEXTLINK), or
 
    (2) directly or indirectly, transfer, sell, lease or otherwise dispose of
       all or substantially all of its assets (determined on a consolidated
       basis for
 
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<PAGE>
       NEXTLINK and its Restricted Subsidiaries taken as a whole and PROVIDED
       that the creation of a Lien on or in any of its assets shall not in and
       of itself constitute the transfer, sale, lease or disposition of the
       assets subject to the Lien),
 
    unless
 
       (a) in a transaction in which NEXTLINK does not survive or in which
              NEXTLINK sells, leases or otherwise disposes of all or
              substantially all of its assets to any other Person, the successor
              entity to NEXTLINK shall be a corporation organized under the laws
              of the United States of America or any State thereof or the
              District of Columbia and shall expressly assume, by a supplemental
              indenture executed and delivered to the trustee in form
              satisfactory to the trustee, all of NEXTLINK's obligations under
              the indenture,
 
       (b) immediately after giving pro forma effect to such transaction as if
              such transaction had occurred at the beginning of the last full
              fiscal quarter immediately prior to the consummation of such
              transaction with the appropriate adjustments with respect to the
              transaction being included in such pro forma calculation and
              treating any Debt which becomes an obligation of NEXTLINK or a
              Subsidiary as a result of such transaction as having been incurred
              by NEXTLINK or such Subsidiary at the time of the transaction, no
              Default or Event of Default shall have occurred and be continuing,
 
       (c) immediately after giving effect to such transaction, the Consolidated
              Net Worth of NEXTLINK (or other successor entity to NEXTLINK) is
              equal to or greater than that of NEXTLINK immediately prior to the
              transaction,
 
       (d) if, as a result of any such transaction, property or assets of
              NEXTLINK would become subject to a Lien prohibited by the
              provisions of the Indenture described under "Covenants--Limitation
              on Liens" above, NEXTLINK or the successor entity to NEXTLINK
              shall have secured the notes as required by said covenant, and
 
       (e) certain other conditions are met. (Section 801)
 
    In the event of any transaction (other than a lease) described in and
complying with the immediately preceding paragraph in which NEXTLINK is not the
surviving Person and the surviving Person assumes all the obligations of
NEXTLINK under the notes and the indenture pursuant to a supplemental indenture,
such surviving Person shall succeed to, and be substituted for, and may exercise
every right and power of, NEXTLINK, and NEXTLINK will be discharged from its
obligations under the indenture and the notes; PROVIDED that solely for the
purpose of calculating amounts described in clause (c) under
"Covenants--Limitations on Restricted Payments," any such surviving Person shall
only be deemed to have succeeded to and be substituted
 
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<PAGE>
for NEXTLINK with respect to the period subsequent to the effective time of such
transaction, and NEXTLINK (before giving effect to such transaction) shall be
deemed to be the "Indenture obligor" for such purposes for all prior periods.
(Section 801)
 
    The meaning of the phrase "all or substantially all" as used above varies
according to the facts and circumstances of the subject transaction, has no
clearly established meaning under relevant law and is subject to judicial
interpretation. Accordingly, in certain circumstances, there may be a degree of
uncertainty in ascertaining whether a particular transaction would involve a
disposition of "all or substantially all" of the assets of NEXTLINK, and
therefore it may be unclear whether the foregoing provisions are applicable.
 
CERTAIN DEFINITIONS
 
    Set forth below is a summary of some of the definitions used in the
Indenture. Reference is made to the Indenture for the definition of all such
terms, as well as any other term used herein for which no definition is
provided. (Section 101)
 
    "Acquired Debt" means, with respect to any specified Person,
 
    (1) Debt of any other Person existing at the time such Person merges with or
       into or consolidates with or becomes a Restricted Subsidiary of such
       specified Person and;
 
    (2) Debt secured by a Lien encumbering any asset acquired by such specified
       Person, which Debt was not Incurred in anticipation of, and was
       outstanding prior to, such merger, consolidation or acquisition.
 
    "Affiliate" of any Person means any other Person directly or indirectly
controlling or controlled by or under direct or indirect common control with
such Person. For the purposes of this definition, "control" when used with
respect to any specified Person means the power to direct the management and
policies of such Person, directly or indirectly, whether through the ownership
of voting securities, by contract or otherwise; and the terms "controlling" and
"controlled" have meanings correlative to the foregoing.
 
    "Asset Disposition" by NEXTLINK or any Restricted Subsidiary means any
transfer, conveyance, sale, lease or other disposition(other than a creation of
a Lien) by such Person (including a consolidation or merger or other sale of any
such Restricted Subsidiary with, into or to another Person in a transaction in
which such Restricted Subsidiary ceases to be a Restricted Subsidiary of
NEXTLINK, but excluding a disposition by a Restricted Subsidiary of NEXTLINK to
NEXTLINK or a Restricted Subsidiary of NEXTLINK or by NEXTLINK to a Restricted
Subsidiary of NEXTLINK) of:
 
    (1) shares of Capital Stock or other ownership interests of a Restricted
       Subsidiary of NEXTLINK, other than as permitted by the provisions of the
       Indenture described above under the Caption "--Limitation on Debt and
 
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       Preferred Stock of Restricted Subsidiaries" or pursuant to a transaction
       in compliance with the covenant described under "Mergers, Consolidations
       and Certain Sales of Assets" above;
 
    (2) substantially all of the assets of NEXTLINK or any of, its Restricted
       Subsidiaries representing a division or line of business (other than as
       part of a Permitted Investment); or
 
    (3) other assets or rights of NEXTLINK or any of its Restricted Subsidiaries
       other than
 
       (a) in the ordinary course of business or
 
       (b) that constitutes a Restricted Payment which is permitted under the
              covenant "--Limitation on Restricted Payments" above; provided
              that a transaction described in clauses (1), (2) and (3) shall
              constitute an Asset Disposition only if the aggregate
              consideration for such transfer, conveyance, sale, lease or other
              disposition is equal to $5 million or more in any 12 month period.
 
    "Attributable Value" means, as to any particular lease under which any
Person is at the time liable other than a Capital Lease Obligation, and at any
date as of which the amount thereof is to be determined, the total net amount of
rent required to be paid by such Person under such lease during the initial term
thereof as determined in accordance with generally accepted accounting
principles, discounted from the last date of such initial term to the date of
determination at a rate per annum equal to the discount rate which would be
applicable to a Capital Lease Obligation with like term in accordance with
generally accepted accounting principles. The net amount of rent required to be
paid under any such lease for any such period shall be the aggregate amount of
rent payable by the lessee with respect to such period after excluding amounts
required to be paid on account of insurance, taxes, assessments, utility,
operating and labor costs and similar charges. In the case of any lease which is
terminable by the lessee upon the payment of penalty, such net amount shall also
include the lesser of the amount of such penalty (in which case no rent shall be
considered as required to be paid under such lease subsequent to the first date
upon which it may be so terminated) or the rent which would otherwise be
required to be paid if such lease is not so terminated. "Attributable Value"
means, as to a Capital Lease Obligation, the principal amount thereof.
 
    "Bank Credit Agreement" means any one or more credit agreements (which may
include or consist of revolving credits) between NEXTLINK or any Restricted
Subsidiary of NEXTLINK and one or more banks or other financial institutions
providing financing for the business of NEXTLINK and its Restricted
Subsidiaries.
 
    "Capital Lease Obligation" of any Person means the obligation to pay rent or
other payment amounts under a lease of (or other Debt arrangements conveying the
right to use) real or personal property of such Person which is required to be
classified and accounted for as a capital lease or a liability on the face of a
balance
 
                                       63
<PAGE>
sheet of such Person in accordance with generally accepted accounting principles
(a "Capital Lease"). The stated maturity of such obligation shall be the date of
the last payment of rent or any other amount due under such lease prior to the
first date upon which such lease may be terminated by the lessee without payment
of a penalty. The principal amount of such obligation shall be the capitalized
amount thereof that would appear on the face of a balance sheet of such Person
in accordance with generally accepted accounting principles.
 
    "Capital Stock" of any Person means any and all shares, interests,
participations or other equivalents (however designated) of corporate stock or
other equity participations, including partnership interests, whether general or
limited, of such Person.
 
    "Common Equity" of any Person means Capital Stock of such Person that is not
Disqualified Stock, and a "sale of Common Equity" includes any sale of Common
Equity effected by private sale or public offering.
 
    "Consolidated Capital Ratio" of any Person as of any date means the ratio of
 
    (1) the aggregate consolidated principal amount of Debt (or in the case of
       Debt issued at a discount the accreted amount thereof) of such Person
       then outstanding (which amount of Debt shall be reduced by any amount of
       cash or cash equivalent collateral securing on a perfected basis and
       dedicated for disbursement exclusively to the payment of principal of and
       interest on such Debt) to
 
    (2) the aggregate consolidated Capital Stock (other than Disqualified Stock)
       and paid in capital (other than in respect of Disqualified Stock) of such
       Person as of such date.
 
    "Consolidated Cash Flow Available for Fixed Charges" for any period means
the Consolidated Net Income of NEXTLINK and its Restricted Subsidiaries for such
period increased by the sum of
 
    (1) Consolidated Interest Expense of NEXTLINK and its Restricted
       Subsidiaries for such period, plus
 
    (2) Consolidated Income Tax Expense of NEXTLINK and its Restricted
       Subsidiaries for such period, plus
 
    (3) the consolidated depreciation and amortization expense included in the
       income statement of NEXTLINK and its Restricted Subsidiaries for such
       period plus
 
    (4) any noncash expense for such period (excluding any noncash charge to the
       extent that it requires an accrual of or a reserve for cash disbursements
       in any future period), plus
 
    (5) any charge related to any premium or penalty paid in connection with
       redeeming or retiring any Debt prior to its stated maturity; PROVIDED,
       HOWEVER,
 
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<PAGE>
       that there shall be excluded therefrom the Consolidated Cash Flow
       Available for Fixed Charges (if positive) of any Restricted Subsidiary of
       NEXTLINK (calculated separately for such Restricted Subsidiary in the
       same manner as provided above for NEXTLINK) that is subject to a
       restriction which prevents the payment of dividends or the making of
       distributions to NEXTLINK or another Restricted Subsidiary of NEXTLINK to
       the extent of such restriction.
 
    "Consolidated Income Tax Expense" for any period means the consolidated
provision for income taxes of NEXTLINK and its Restricted Subsidiaries for such
period calculated on a consolidated basis in accordance with generally accepted
accounting principles.
 
    "Consolidated Interest Expense" means for any period the consolidated
interest expense included in a consolidated income statement (excluding interest
income) of NEXTLINK and its Restricted Subsidiaries for such period calculated
on a consolidated basis in accordance with generally accepted accounting
principles, including without limitation or duplication (or, to the extent not
so included, with the addition of):
 
    (1) the amortization of Debt discounts;
 
    (2) any payments or fees with respect to letters of credit, bankers'
       acceptances or similar facilities;
 
    (3) fees with respect to interest rate swap or similar agreements or foreign
       currency hedge, exchange or similar agreements;
 
    (4) Preferred Dividends of NEXTLINK and its Restricted Subsidiaries (other
       than dividends paid in shares of Preferred Stock that is not Disqualified
       Stock) declared and paid or payable;
 
    (5) accrued Disqualified Stock dividends of NEXTLINK and its Restricted
       Subsidiaries, whether or not declared or paid;
 
    (6) interest on Debt guaranteed by NEXTLINK and its Restricted Subsidiaries;
       and
 
    (7) the portion of any Capital Lease Obligation paid or accrued during such
       period that is allocable to interest expense.
 
    "Consolidated Net Income" for any period means the consolidated net income
(or loss) of NEXTLINK and its Restricted Subsidiaries for such period determined
on a consolidated basis in accordance with generally accepted accounting
principles; PROVIDED that there shall be excluded therefrom:
 
    (1) the net income (or loss) of any Person acquired by NEXTLINK or a
       Restricted Subsidiary of NEXTLINK in a pooling of interests transaction
       for any period prior to the date of such transaction;
 
                                       65
<PAGE>
    (2) the net income (or loss) of any Person that is not a Restricted
       Subsidiary of NEXTLINK except to the extent of the amount of dividends or
       other distributions actually paid to NEXTLINK or a Restricted Subsidiary
       of NEXTLINK by such Person during such period;
 
    (3) gains or losses on Asset Dispositions by NEXTLINK or its Restricted
       Subsidiaries;
 
    (4) all extraordinary gains and extraordinary losses;
 
    (5) the cumulative effect of changes in accounting principles;
 
    (6) noncash gains or losses resulting from fluctuations in currency exchange
       rates;
 
    (7) any noncash gain or loss realized on the termination of any employee
       pension benefit plan; and
 
    (8) the tax effect of any of the items described in clauses (1) through (8)
       above.
 
PROVIDED, FURTHER, that for purposes of any determination pursuant to the
provisions described under "Covenants--Limitation on Restricted Payments," there
shall further be excluded therefrom the net income (but not net loss) of any
Restricted Subsidiary of NEXTLINK that is subject to a restriction which
prevents the payment of dividends or the making of distributions to NEXTLINK or
another Restricted Subsidiary of NEXTLINK to the extent of such restriction.
 
    "Consolidated Net Worth" of any Person means the consolidated stockholders'
equity of such Person, determined on a consolidated basis in accordance with
generally accepted accounting principles, less amounts attributable to
Disqualified Stock of such Person; PROVIDED that, with respect to NEXTLINK,
adjustments following the date of the Indenture to the accounting books and
records of NEXTLINK in accordance with Accounting Principles Board Opinions Nos.
16 and 17 (or successor opinions thereto) or otherwise resulting from the
acquisition of control of NEXTLINK by another Person shall not be given effect
to.
 
    "Consolidated Tangible Assets" of any Person means the total amount of
assets (less applicable reserves and other properly deductible items) which
under generally accepted accounting principles would be included on a
consolidated balance sheet of such Person and its Restricted Subsidiaries after
deducting therefrom all goodwill, trade names, trademarks, patents, unamortized
debt discount and expense and other like intangibles, which in each case under
generally accepted accounting principles would be included on such consolidated
balance sheet; PROVIDED that, with respect to NEXTLINK, adjustments following
the date of the Indenture to the accounting books and records of NEXTLINK in
accordance with Accounting Principles Board Opinions Nos. 16 and 17 (or
successor opinions thereto) or otherwise resulting from the acquisition of
control of NEXTLINK by another Person shall not be given effect to.
 
                                       66
<PAGE>
    "Debt" means (without duplication), with respect to any Person, whether
recourse is to all or a portion of the assets of such Person and whether or not
contingent:
 
    (1) every obligation of such Person for money borrowed;
 
    (2) every obligation of such Person evidenced by bonds, debentures, notes or
       other similar instruments, including any such obligations Incurred in
       connection with the acquisition of property, assets or businesses;
 
    (3) every reimbursement obligation of such Person with respect to letters of
       credit, bankers' acceptances or similar facilities issued for the account
       of such Person;
 
    (4) every obligation of such Person issued or assumed as the deferred
       purchase price of property or services (including securities repurchase
       agreements but excluding trade accounts payable or accrued liabilities
       arising in the ordinary course of business which are not overdue or which
       are being contested in good faith);
 
    (5) every Capital Lease Obligation of such Person;
 
    (6) all Receivables Sales of such Person, together with any obligation of
       such Person to pay any discount, interest, fees, indemnities, penalties,
       recourse, expenses or other amounts in connection therewith;
 
    (7) all obligations to redeem Disqualified Stock issued by such Person;
 
    (8) every obligation under Interest Rate and Currency Protection Agreements
       of such Person; and
 
    (9) every obligation of the type referred to in clauses (1) through (8) of
       another Person and all dividends of another Person the payment of which,
       in either case, such Person has Guaranteed.
 
    The "amount" or "principal amount" of Debt at any time of determination as
used herein represented by
 
    (1) any Debt issued at a price that is less than the principal amount at
       maturity thereof, shall be the amount of the liability in respect thereof
       determined in accordance with generally accepted accounting principles,
 
    (2) any Receivables Sale, shall be the amount of the unrecovered capital or
       principal investment of the purchaser (other than NEXTLINK or a Wholly
       Owned Restricted Subsidiary of NEXTLINK) thereof, excluding amounts
       representative of yield or interest earned on such investment,
 
    (3) any Disqualified Stock, shall be the maximum fixed redemption or
       repurchase price in respect thereof,
 
    (4) any Capital Lease Obligation, shall be determined in accordance with the
       definition thereof, or
 
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<PAGE>
    (5) any Permitted Interest Rate or Currency Protection Agreement, shall be
       zero. In no event shall Debt include any liability for taxes.
 
    "Default" means an event that with the passing of time or the giving of
notice or both shall constitute an Event of Default.
 
    "Disqualified Stock" of any Person means any Capital Stock of such Person
(other than Capital Stock outstanding on the Issue Date) which, by its terms (or
by the terms of any security into which it is convertible or for which it is
exchangeable), or upon the happening of any event, matures or is mandatorily
redeemable, pursuant to a sinking fund obligation or otherwise, or is redeemable
at the option of the holder thereof, in whole or in part, on or prior to the
final Stated Maturity of the notes; PROVIDED, HOWEVER, that any Preferred Stock
which would not constitute Disqualified Stock but for provisions thereof giving
holders thereof the right to require NEXTLINK to repurchase or redeem such
Preferred Stock upon the occurrence of an asset sale or a Change of Control
occurring prior to the final Stated Maturity of the notes shall not constitute
Disqualified Stock if the asset sale or change of control provisions applicable
to such Preferred Stock are no more favorable to the holders of such Preferred
Stock than the provisions applicable to the notes contained in the covenant
described under "Covenants--Limitation on Asset Dispositions" or
"Covenants--Change of Control" and such Preferred Stock specifically provides
that NEXTLINK will not repurchase or redeem any such stock pursuant to such
provisions prior to NEXTLINK's repurchase of such notes as are required to be
repurchased pursuant to the covenant described under "Covenants--Limitation on
Asset Dispositions" or "Covenants--Change of Control".
 
    "Eligible Institution" means a commercial banking institution that has
combined capital and surplus of not less than $500 million or its equivalent in
foreign currency, whose debt is rated "A 3" or higher, "A" or higher or "A" or
higher according to Moody's Investors Service, Inc., Standard & Poor's Ratings
Group or Duff & Phelps Credit Rating Co. (or such similar equivalent rating by
at least one "nationally recognized statistical rating organization" (as defined
in Rule 436 under the Securities Act)) respectively, at the time as of which any
investment or rollover therein is made.
 
    "Eligible Receivables" means, at any time, Receivables of NEXTLINK and its
Restricted Subsidiaries, as evidenced on the most recent quarterly consolidated
balance sheet of NEXTLINK as at a date at least 45 days prior to such time
arising in the ordinary course of business of NEXTLINK or any Restricted
Subsidiary of NEXTLINK.
 
    "Event of Default" has the meaning set forth under "Events of Default"
below.
 
    "Exchange Act" means the Securities Exchange Act of 1934, as amended (or any
successor act) and the rules and regulations thereunder.
 
    "Government Securities" means direct obligations of, or obligations
guaranteed by, the United States of America for the payment of which obligations
or guarantee the full faith and credit of the United States is pledged and which
have a remaining
 
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<PAGE>
weighted average life to maturity of not more than 18 months from the date of
Investment therein.
 
    "Guarantee" by any Person means any obligation, contingent or otherwise, of
such Person guaranteeing, or having the economic effect of guaranteeing, any
Debt of any other Person (the "primary obligor") in any manner, whether directly
or indirectly, and including, without limitation, any obligation of such Person:
 
    (1) to purchase or pay (or advance or supply funds for the purchase or
       payment of) such Debt or to purchase (or to advance or supply funds for
       the purchase of) any security for the payment of such Debt;
 
    (2) to purchase property, securities or services for the purpose of assuring
       the holder of such Debt of the payment of such Debt; or
 
    (3) to maintain working capital, equity capital or other financial statement
       condition or liquidity of the primary obligor so as to enable the primary
       obligor to pay such Debt (and "Guaranteed", "Guaranteeing" and
       "Guarantor" shall have meanings correlative to the foregoing):
 
PROVIDED, HOWEVER, that the Guarantee by any Person shall not include
endorsements by such Person for collection or deposit, in either case, in the
ordinary course of business; and PROVIDED FURTHER, that the incurrence by a
Restricted Subsidiary of NEXTLINK of a lien permitted under clause (4) of the
second paragraph of the "Limitation on Liens" covenant shall not be deemed to
constitute a Guarantee by such Restricted Subsidiary of any Purchase Money Debt
of NEXTLINK secured thereby.
 
    "Incur" means, with respect to any Debt or other obligation of any Person,
to create, issue, incur (by conversion, exchange or otherwise), assume,
Guarantee or otherwise become liable in respect of such Debt or other obligation
including by acquisition of Subsidiaries or the recording, as required pursuant
to generally accepted accounting principles or otherwise, of any such Debt or
other obligation on the balance sheet of such Person (and "Incurrence",
"Incurred", "Incurrable" and "Incurring" shall have meanings correlative to the
foregoing); PROVIDED, HOWEVER, that a change in generally accepted accounting
principles that results in an obligation of such Person that exists at such time
becoming Debt shall not be deemed an Incurrence of such Debt and that neither
the accrual of interest nor the accretion of original issue discount shall be
deemed an Incurrence of Debt; PROVIDED, FURTHER, however, that NEXTLINK may
elect to treat all or any portion of revolving credit debt of NEXTLINK or a
Subsidiary as being Incurred from and after any date beginning the date the
revolving credit commitment is extended to NEXTLINK or a Subsidiary, by
furnishing notice thereof to the Trustee, and any borrowings or reborrowings by
NEXTLINK or a Subsidiary under such commitment up to the amount of such
commitment designated by NEXTLINK as Incurred shall not be deemed to be new
lncurrences of Debt by NEXTLINK or such Subsidiary.
 
                                       69
<PAGE>
    "Interest Rate or Currency Protection Agreement" of any Person means any
forward contract, futures contract, swap, option or other financial agreement or
arrangement (including, without limitation, caps, floors, collars and similar
agreements) relating to, or the value of which is dependent upon, interest rates
or currency exchange rates or indices.
 
    "Investment" by any Person means any direct or indirect loan, advance or
other extension of credit or capital contribution (by means of transfers of cash
or other property to others or payments for property or services for the account
or use of others, or otherwise) to, or purchase or acquisition of Capital Stock,
bonds, notes, debentures or other securities or evidence of Debt issued by, any
other Person, including any payment on a Guarantee of any obligation of such
other Person, but excluding any loan, advance or extension of credit to an
employee of NEXTLINK or any of its Restricted Subsidiaries in the ordinary
course of business, accounts receivables and other commercially reasonable
extensions of trade credit.
 
    "Issue Date" means November 12, 1998.
 
    "Joint Venture" means a corporation, partnership or other entity engaged in
one or more Telecommunications Businesses as to which NEXTLINK (directly or
through one or more Restricted Subsidiaries) exercises managerial control and in
which NEXTLINK owns
 
    (1) a 50% or greater interest, or
 
    (2) a 30% or greater interest, together with options or other contractual
       rights, exercisable not more than seven years after NEXTLINK's initial
       Investment in such Joint Venture, to increase its interest to not less
       than 50%.
 
    "Lien" means, with respect to any property or assets, any mortgage or deed
of trust, pledge, hypothecation, assignment, Receivables Sale, deposit
arrangement, security interest, lien, charge, easement (other than any easement
not materially impairing usefulness or marketability), encumbrance, preference,
priority or other security agreement or preferential arrangement of any kind or
nature whatsoever on or with respect to such property or assets (including,
without limitation, any conditional sale or other title retention agreement
having substantially the same economic effect as any of the foregoing).
 
    "Marketable Securities" means:
 
    (1) Government Securities;
 
    (2) any time or demand deposit account, money market deposit and certificate
       of deposit maturing not more than 365 days after the date of acquisition
       issued by, or time deposit of, an Eligible Institution;
 
    (3) commercial paper maturing not more than 365 days after the date of
       acquisition issued by a corporation (other than an Affiliate of NEXTLINK)
       with a rating, at the time as of which any investment therein is made, of
 
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<PAGE>
       "P1" or higher according to Moody's Investors Service, Inc., "A1" or
       higher according to Standard & Poor's Ratings Group or "A1" or higher
       according to Duff & Phelps Credit Rating Co. (or such similar equivalent
       rating by at least one "nationally recognized statistical rating
       organization" (as defined in Rule 436 under the Securities Act));
 
    (4) any banker's acceptances or money market deposit accounts issued or
       offered by an Eligible Institution;
 
    (5) repurchase obligations with a term of not more than 7 days for
       Government Securities entered into with an Eligible Institution;
 
    (6) auction rate preferred stocks of any corporation maturing within 90 days
       after the date of acquisition by NEXTLINK thereof, having a rating of at
       least AA by Standard & Poor's; and
 
    (7) any fund investing exclusively in investments of the types described in
       clauses (1) through (6) above.
 
    "Net Available Proceeds" from any Asset Disposition by any Person means cash
or readily marketable cash equivalents received (including by way of sale or
discounting of a note, installment receivable or other receivable, but excluding
any other consideration received in the form of assumption by the acquiror of
Debt or other obligations relating to such properties or assets) therefrom by
such Person, net of:
 
    (1) all legal, title and recording tax expenses, commissions and other fees
       and expenses Incurred and all federal, state, provincial, foreign and
       local taxes (including taxes payable upon payment or other distribution
       of funds from a foreign subsidiary to NEXTLINK or another Subsidiary of
       NEXTLINK) required to be accrued as a liability as a consequence of such
       Asset Disposition;
 
    (2) all payments made by such Person or its Restricted Subsidiaries on any
       Debt which is secured by such assets in accordance with the terms of any
       Lien upon or with respect to such assets or which must by the terms of
       such Lien, or in order to obtain a necessary consent to such Asset
       Disposition or by applicable law, be repaid out of the proceeds from such
       Asset Disposition;
 
    (3) all distributions and other payments made to minority interest holders
       in Restricted Subsidiaries of such Person or joint ventures as a result
       of such Asset Disposition;
 
    (4) appropriate amounts to be provided by such Person or any Restricted
       Subsidiary thereof, as the case may be, as a reserve in accordance with
       generally accepted accounting principles against any liabilities
       associated with such assets and retained by such Person or any Restricted
       Subsidiary thereof, as the case may be, after such Asset Disposition,
       including, without limitation, liabilities under any indemnification
       obligations and severance and
 
                                       71
<PAGE>
       other employee termination costs associated with such Asset Disposition,
       in each case as determined by the Board of Directors of NEXTLINK, in its
       reasonable good faith judgment evidenced by a Board Resolution filed with
       the Trustee; PROVIDED, HOWEVER, that any reduction in such reserve within
       twelve months following the consummation of such Asset Disposition will
       be treated for all purposes of the Indenture and the Notes as a new Asset
       Disposition at the time of such reduction with Net Available Proceeds
       equal to the amount of such reduction; and
 
    (5) any consideration for an Asset Disposition (which would otherwise
       constitute Net Available Proceeds) that is required to be held in escrow
       pending determination of whether a purchase price adjustment will be
       made, but amounts under this clause shall become Net Available Proceeds
       at such time and to the extent such amounts are released to such Person.
 
    "Offer to Purchase" means a written offer (the "Offer") sent by NEXTLINK by
first class mail, postage prepaid, to each holder at his address appearing in
the Note Register on the date of the Offer describing the transaction or
transactions necessitating the Offer and offering to purchase up to the
principal amount of Notes specified in such Offer at the purchase price
specified in such Offer (as determined pursuant to the Indenture). Unless
otherwise required by applicable law, the Offer shall specify an expiration date
(the "Expiration Date") of the Offer to Purchase which shall be, subject to any
contrary requirements of applicable law, not less than 30 days or more than 60
days after the date of such Offer and a settlement date (the "Purchase Date")
for purchase of Notes within five Business Days after the Expiration Date. The
Offer shall contain all instructions and materials necessary to enable the
holders to tender Notes pursuant to the Offer to Purchase.
 
    "Permitted Interest Rate or Currency Protection Agreement" of any Person
means any Interest Rate or Currency Protection Agreement entered into with one
or more financial institutions in the ordinary course of business that is
designed to protect such Person against fluctuations in interest rates or
currency exchange rates with respect to Debt Incurred and which shall have a
notional amount no greater than the payments due with respect to the Debt being
hedged thereby and not for purposes of speculation.
 
    "Permitted Investment" means:
 
    (1) any Investment in a Joint Venture (including the purchase or acquisition
       of any Capital Stock of a Joint Venture), provided the aggregate amount
       of all outstanding Investments pursuant to this clause (1) in Joint
       Ventures in which NEXTLINK owns, directly or indirectly, a less than 50%
       interest shall not exceed $25 million;
 
    (2) any Investment in any Person as a result of which such Person becomes a
       Restricted Subsidiary or, subject to the proviso to clause (1) of this
       definition, becomes a Joint Venture of NEXTLINK;
 
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<PAGE>
    (3) any Investment in Marketable Securities,
 
    (4) Investments in Permitted Interest Rate or Currency Protection
       Agreements;
 
    (5) Investments made as a result of the receipt of noncash consideration
       from an Asset Disposition that was made pursuant to and in compliance
       with the covenant described under "Covenants--Limitation on Asset
       Dispositions" above; and
 
    (6) other Investments in an aggregate amount not to exceed the aggregate net
       proceeds received by NEXTLINK or any Restricted Subsidiary after the date
       of the Indenture from the sale or liquidation of any Unrestricted
       Subsidiary or any interest therein (except to the extent that any such
       amount is included in the calculation of Consolidated Net Income).
 
    "Permitted Liens" means:
 
    (1) Liens for taxes, assessments, governmental charges or claims which are
       not yet delinquent or which are being contested in good faith by
       appropriate proceedings, if a reserve or other appropriate provision, if
       any, as shall be required in conformity with generally accepted
       accounting principles shall have been made therefor;
 
    (2) other Liens incidental to the conduct of NEXTLINK's and its Restricted
       Subsidiaries' business or the ownership of its property and assets not
       securing any Debt, and which do not in the aggregate materially detract
       from the value of NEXTLINK's and its Restricted Subsidiaries' property or
       assets when taken as a whole, or materially impair the use thereof in the
       operation of its business;
 
    (3) Liens with respect to assets of a Restricted Subsidiary granted by such
       Restricted Subsidiary to NEXTLINK to secure Debt owing to NEXTLINK;
 
    (4) pledges and deposits made in the ordinary course of business in
       connection with workers' compensation, unemployment insurance and other
       types of statutory obligations (including to secure government
       contracts);
 
    (5) deposits made to secure the performance of tenders, bids, leases, and
       other obligations of like nature incurred in the ordinary course of
       business (exclusive of obligations for the payment of borrowed money);
 
    (6) zoning restrictions, servitudes, easements, rights-of-way, restrictions
       and other similar charges or encumbrances incurred in the ordinary course
       of business which, in the aggregate, do not materially detract from the
       value of the property subject thereto or interfere with the ordinary
       conduct of the business of NEXTLINK or its Restricted Subsidiaries;
 
    (7) Liens arising out of judgments or awards against NEXTLINK or any
       Restricted Subsidiary with respect to which NEXTLINK or such Restricted
       Subsidiary is prosecuting an appeal or proceeding for review and
 
                                       73
<PAGE>
       NEXTLINK or such Restricted Subsidiary is maintaining adequate reserves
       in accordance with generally accepted accounting principles;
 
    (8) any interest or title of a lessor in the property subject to any lease
       other than a Capital Lease; and
 
    (9) any statutory warehousemen's, materialmen's or other similar Liens for
       sums not then due and payable (or which, if due and payable, are being
       contested in good faith and with respect to which adequate reserves are
       being maintained to the extent required by generally accepted accounting
       principles).
 
    "Person" means any individual, corporation, partnership, limited liability
company, joint venture, association, joint stock company, trust, unincorporated
organization, government or agency or political subdivision thereof or any other
entity.
 
    "Preferred Dividends" for any Person means for any period the quotient
determined by dividing the amount of dividends and distributions paid or accrued
(whether or not declared) on Preferred Stock of such Person during such period
calculated in accordance with generally accepted accounting principles, by 1
minus the maximum statutory income tax rate then applicable to NEXTLINK
(expressed as a decimal).
 
    "Preferred Stock" of any Person means Capital Stock of such Person of any
class or classes (however designated) that ranks prior, as to the payment of
dividends or as to the distribution of assets upon any voluntary or involuntary
liquidation, dissolution or winding up of such Person, to shares of Capital
Stock of any other class of such Person.
 
    "Purchase Money Debt" means
 
    (1) Acquired Debt Incurred in connection with the acquisition of
       Telecommunications Assets and
 
    (2) Debt of NEXTLINK or of any Restricted Subsidiary of NEXTLINK (including,
       without limitation, Debt represented by Bank Credit Agreements, Capital
       Lease Obligations, Vendor Financing Facilities, mortgage financings and
       purchase money obligations) Incurred for the purpose of financing all or
       any part of the cost of construction, acquisition or improvement by
       NEXTLINK or any Restricted Subsidiary of NEXTLINK or any Joint Venture of
       any Telecommunications Assets of NEXTLINK, any Restricted Subsidiary of
       NEXTLINK or any Joint Venture, and including any related notes,
       Guarantees, collateral documents, instruments and agreements executed in
       connection therewith, as the same may be amended, supplemented, modified
       or restated from time to time.
 
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<PAGE>
    "Receivables" means receivables, chattel paper, instruments, documents or
intangibles evidencing or relating to the right to payment of money in respect
of the sale of goods or services.
 
    "Receivables Sale" of any Person means any sale of Receivables of such
Person (pursuant to a purchase facility or otherwise), other than in connection
with a disposition of the business operations of such Person relating thereto or
a disposition of defaulted Receivables for purpose of collection and not as a
financing arrangement.
 
    "Related Person" of any Person means any other Person directly or indirectly
owning
 
    (1) 10% or more of the Outstanding Common Equity of such Person (or, in the
       case of a Person that is not a corporation, 10% or more of the equity
       interest in such Person) or
 
    (2) 10% or more of the combined voting power of the Voting Stock of such
       Person.
 
    "Restricted Subsidiary" of NEXTLINK means any Subsidiary, whether existing
on or after the date of the Indenture, unless such Subsidiary is an Unrestricted
Subsidiary.
 
    "Sale and Leaseback Transaction" of any Person means an arrangement with any
lender or investor or to which such lender or investor is a party providing for
the leasing by such Person of any property or asset of such Person which has
been or is being sold or transferred by such Person more than 365 days after the
acquisition thereof or the completion of construction or commencement of
operation thereof to such lender or investor or to any person to whom funds have
been or are to be advanced by such lender or investor on the security of such
property or asset. The stated maturity of such arrangement shall be the date of
the last payment of rent or any other amount due under such arrangement prior to
the first date on which such arrangement may be terminated by the lessee without
payment of a penalty.
 
    "Significant Subsidiary" means a Restricted Subsidiary that is a
"significant subsidiary" as defined in Rule 102(w) of Regulation S-X under the
Securities Act and the Exchange Act.
 
    "Subordinated Debt" means Debt of NEXTLINK as to which the payment of
principal of (and premium, if any) and interest and other payment obligations in
respect of such Debt shall be subordinate to the prior payment in full of the
Notes to at least the following extent:
 
    (1) no payments of principal of (or premium, if any) or interest on or
       otherwise due in respect of such Debt may be permitted for so long as any
       default in the payment of principal (or premium, if any) or interest on
       the Notes exists;
 
    (2) in the event that any other default that with the passing of time or the
       giving of notice, or both, would constitute an Event of Default exists
       with respect to
 
                                       75
<PAGE>
       the notes, upon notice by 25% or more in principal amount of the Notes to
       the trustee, the trustee shall have the right to give notice to NEXTLINK
       and the holders of such Debt (or trustees or agents therefor) of a
       payment blockage, and thereafter no payments of principal of (or premium,
       if any) or interest on or otherwise due in respect of such Debt may be
       made for a period of 179 days from the date of such notice or for the
       period until such default has been cured or waived or ceased to exist and
       any acceleration of the notes has been rescinded or annulled, whichever
       period is shorter (which Debt may provide that no new period of payment
       blockage may be commenced by a payment blockage notice unless and until
       360 days have elapsed since the effectiveness of the immediately prior
       notice, no nonpayment default that existed or was continuing on the date
       of delivery of any payment blockage notice to such holders (or such
       agents or trustees) shall be, or be made, the basis for a subsequent
       payment blockage notice and failure of NEXTLINK to make payment on such
       Debt when due or within any applicable grace period, whether or not on
       account of such payment blockage provisions, shall constitute an event of
       default thereunder); and
 
    (3) such Debt may not provide for payments of principal of such Debt at the
       stated maturity thereof or by way of a sinking fund applicable thereto or
       by way of any mandatory redemption, defeasance, retirement or repurchase
       thereof by NEXTLINK (including any redemption, retirement or repurchase
       which is contingent upon events or circumstances, but executing any
       retirement required by virtue of acceleration of such Debt upon an event
       of default thereunder), in each case prior to the final Stated Maturity
       of the notes or permit redemption or other retirement (including pursuant
       to an offer to purchase made by NEXTLINK) of such other Debt at the
       option of the holder thereof prior to the final Stated Maturity of the
       notes, other than a redemption or other retirement at the option of the
       holder of such Debt (including pursuant to an offer to purchase made by
       NEXTLINK) which is conditioned upon a change of control of NEXTLINK
       pursuant to provisions substantially similar to those described under
       "Covenants--Change of Control" (and which shall provide that such Debt
       will not be repurchased pursuant to such provisions prior to NEXTLINK's
       repurchase of the notes required to be repurchased by NEXTLINK pursuant
       to the provisions described under "Covenants--Change of Control").
 
    "Subsidiary" of any Person means
 
    (1) a corporation more than 50% of the combined voting power of the
       outstanding Voting Stock of which is owned, directly or indirectly, by
       such Person or by one or more other Subsidiaries of such Person or by
       such Person and one or more Subsidiaries thereof or
 
    (2) any other Person (other than a corporation) in which such Person, or one
       or more other Subsidiaries of such Person or such Person and one or more
 
                                       76
<PAGE>
       other Subsidiaries thereof, directly or indirectly, has at least a
       majority ownership and power to direct the policies, management and
       affairs thereof.
 
    "Telecommunications Assets" means all assets, rights (contractual or
otherwise) and properties, whether tangible or intangible, used or intended for
use in connection with a Telecommunications Business.
 
    "Telecommunications Business" means the business of
 
(1) transmitting, or providing services relating to the transmission of, voice,
    video or data through owned or leased transmission facilities,
 
(2) creating, developing or marketing communications related network equipment,
    software and other devices for use in a Telecommunication Business or
 
(3) evaluating, participating or pursuing any other activity or opportunity that
    is primarily related to those identified in (1) or (2) above and shall, in
    any event, include all businesses in which NEXTLINK or any of its
    Subsidiaries are engaged on the Issue Date; provided that the determination
    of what constitutes a Telecommunications Business shall be made in good
    faith by the Board of Directors of NEXTLINK, which determination shall be
    conclusive.
 
    "Unrestricted Subsidiary" means
 
(1) any Subsidiary of NEXTLINK designated as such by the Board of Directors of
    NEXTLINK as set forth below where
 
    (a) neither NEXTLINK nor any of its other Subsidiaries (other than another
       Unrestricted Subsidiary)
 
       (A) provides credit support for, or Guarantee of, any Debt of such
              Subsidiary or any Subsidiary of such Subsidiary (including any
              undertaking, agreement or instrument evidencing such Debt) or
 
       (B) is directly or indirectly liable for any Debt of such Subsidiary or
              any Subsidiary of such Subsidiary, and
 
    (b) no default with respect to any Debt of such Subsidiary or any Subsidiary
       of such Subsidiary (including any right which the holders thereof may
       have to take enforcement action against such Subsidiary) would permit
       (upon notice, lapse of time or both) any holder of any other Debt of
       NEXTLINK and its Restricted Subsidiaries to declare a default on such
       other Debt or cause the payment thereof to be accelerated or payable
       prior to its final scheduled maturity and
 
(2) any Subsidiary of an Unrestricted Subsidiary.
 
    The Board of Directors of NEXTLINK may designate any Subsidiary to be an
Unrestricted Subsidiary unless such Subsidiary owns any Capital Stock of, or
owns or holds any Lien on any property of, any other Subsidiary of NEXTLINK
which is not a
 
                                       77
<PAGE>
Subsidiary of the Subsidiary to be so designated or otherwise an Unrestricted
Subsidiary, PROVIDED that either
 
       (a) the Subsidiary to be so designated has total assets of $1,000 or less
              or
 
       (b) immediately after giving effect to such designation, NEXTLINK could
              Incur at least $1.00 of additional Debt pursuant to the first
              paragraph under "Covenants--Limitation on Consolidated
              Indebtedness" above and provided, further, that NEXTLINK could
              make a Restricted Payment in an amount equal to the greater of the
              fair market value and the book value of such Subsidiary pursuant
              to the covenant described under "Covenants--Limitation on
              Restricted Payments" and such amount is thereafter treated as a
              Restricted Payment for the purpose of calculating the aggregate
              amount available for Restricted Payments thereunder. The Board of
              Directors of NEXTLINK may designate any Unrestricted Subsidiary to
              be a Restricted Subsidiary, PROVIDED that, if such Unrestricted
              Subsidiary has Debt outstanding at such time, either
 
              (A) immediately after giving effect to such designation, NEXTLINK
                  could Incur at least $1.00 of additional Debt pursuant to the
                  first paragraph under "Covenants--Limitation on Consolidated
                  Indebtedness" above or
 
              (B) NEXTLINK or such Restricted Subsidiary could Incur such Debt
                  hereunder (other than as Acquired Debt).
 
    "Vendor Financing Facility" means any agreements between NEXTLINK or a
Restricted Subsidiary and one or more vendors or lessors of equipment or other
capital assets to NEXTLINK or any of its Restricted Subsidiaries (or any
affiliate of any such vendor or lessor) providing financing for the acquisition
by NEXTLINK or any such Restricted Subsidiary of equipment or other capital
assets from any such vendor or lessor.
 
    "Voting Stock" of any Person means Capital Stock of such Person which
ordinarily has voting power for the election of directors (or persons performing
similar functions) of such Person, whether at all times or only so long as no
senior class of securities has such voting power by reason of any contingency.
 
    "Wholly Owned Restricted Subsidiary" of any Person means a Restricted
Subsidiary of such Person 99% or more of the outstanding Capital Stock or other
ownership interests of which (other than directors' qualifying shares) shall at
the time be owned by such Person or by one or more Wholly Owned Restricted
Subsidiaries of such Person or by such Person and one or more Wholly Owned
Restricted Subsidiaries of such Person.
 
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<PAGE>
EVENTS OF DEFAULT
 
    The following are Events of Default under the indenture:
 
    (1) failure to pay principal of (or premium, if any, on) any note when due;
 
    (2) failure to pay any interest on any note when due, continued for 30 days;
 
    (3) default in the payment of principal and interest on notes required to be
       purchased pursuant to an Offer to Purchase as described under
       "Covenants--Change of Control" when due and payable;
 
    (4) failure to perform or comply with the provisions described under
       "Mergers, Consolidations and Certain Sales of Assets";
 
    (5) failure to perform any other covenant or agreement of NEXTLINK under the
       Indenture or the notes continued for 60 days after written notice to
       NEXTLINK by the Trustee or Holders of at least 25% in aggregate principal
       amount of outstanding notes;
 
    (6) default under the terms of any instrument evidencing or securing Debt of
       NEXTLINK or any Significant Subsidiary having an outstanding principal
       amount of $10 million individually or in the aggregate which default
       results in the acceleration of the payment of such Debt or constitutes
       the failure to pay such Debt when due;
 
    (7) the rendering of a final judgment or judgments (not subject to appeal)
       for the payment of money against NEXTLINK or any Significant Subsidiary
       in an aggregate amount in excess of $10 million which remains
       undischarged or unstayed for a period of 45 days after the date on which
       the right to appeal all such judgments has expired; and
 
    (8) certain events of bankruptcy, insolvency or reorganization affecting
       NEXTLINK or any Significant Subsidiary. (Section 501)
 
    Subject to the provisions of the indenture relating to the duties of the
trustee in case an Event of Default shall occur and be continuing, the trustee
will be under no obligation to exercise any of its rights or powers under the
indenture at the request or direction of any of the holders, unless such holders
shall have offered to the trustee reasonable indemnity. (Section 603) Subject to
such provisions for the indemnification of the trustee, the holders of a
majority in aggregate principal amount of the outstanding notes will have the
right to direct the time, method and place of conducting any proceeding for any
remedy available to the trustee or exercising any trust or power conferred on
the trustee. The trustee may refuse, however, to follow any direction that the
trustee, in its sole discretion, determines may be unduly prejudicial to the
rights of another holder or that may subject the trustee to any liability or
expense if the trustee determines, in its sole discretion, that it lacks
indemnification against such loss or expense. (Section 512)
 
                                       79
<PAGE>
    If an Event of Default (other than an Event of Default described in Clause
(8) above with respect to NEXTLINK) shall occur and be continuing, either the
trustee or the holders of at least 25% in aggregate principal amount of the
outstanding notes at maturity may accelerate the maturity of all notes;
PROVIDED, HOWEVER, that after such acceleration, but before a judgment or decree
based on acceleration, the holders of a majority in aggregate principal amount
at maturity of outstanding notes may, under certain circumstances, rescind and
annul such acceleration if all Events of Default, other than the nonpayment of
accelerated principal, have been cured or waived as provided in the indenture.
If an Event of Default specified in Clause (8) above occurs with respect to
NEXTLINK, the outstanding Notes will IPSO FACTO become immediately due and
payable without any declaration or other act on the part of the trustee or any
holder. (Section 502) For information as to waiver of defaults, see
"Modification and Waiver".
 
    No holder of any note will have any right to institute any proceeding with
respect to the indenture or for any remedy thereunder, unless such holder shall
have previously given to the trustee written notice of a continuing Event of
Default (as defined) and unless also the holders of at least 25% in aggregate
principal amount of the outstanding notes shall have made written request, and
offered reasonable indemnity, to the trustee to institute such proceeding as
trustee, and the trustee shall not have received from the holders of a majority
in aggregate principal amount of the outstanding notes a direction inconsistent
with such request and shall have failed to institute such proceeding within 60
days. (Section 507) However, such limitations do not apply to a suit instituted
by a holder of a note for enforcement of payment of the principal of and
premium, if any, or interest on such Note on or after the respective due dates
expressed in such Note. ( Section508)
 
    The indenture provides that if a Default occurs and is continuing, generally
the Trustee must, within 90 days after the occurrence of such Default, give to
the holders notice of such Default. The Trustee may withhold from holders of the
notes notice of any continuing Default or Event of Default (except a Default or
Event of Default relating to the payment of principal of, premium, if any or
interest) if it determines that withholding notice is in their interest;
PROVIDED, HOWEVER, that in the case of any default of a character specified in
Clause (e) above, no such notice to holders shall be given until at least 30
days after the occurrence thereof. (Section 602)
 
    NEXTLINK will be required to furnish to the trustee quarterly a statement as
to the performance by NEXTLINK of certain of its obligations under the Indenture
and NEXTLINK is required upon becoming aware of any Default or Event of Default
to deliver to the trustee a statement specifying such Default or Event of
Default. (Section 1018)
 
SATISFACTION AND DISCHARGE OF THE INDENTURE
 
    The indenture will cease to be of further effect as to all outstanding notes
(except as to
 
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<PAGE>
    (1) rights of registration of transfer and exchange and NEXTLINK's right of
       optional redemption,
 
    (2) substitution of apparently mutilated, defaced, destroyed, lost or stolen
       notes,
 
    (3) rights of holders to receive payment of principal of and premium, if
       any, and interest on the Notes,
 
    (4) rights, obligations and immunities of the trustee under the indenture
       and
 
    (5) rights of the holders of the notes as beneficiaries of the Indenture
       with respect to any property deposited with the trustee payable to all or
       any of them), if
 
       (a) NEXTLINK will have paid or caused to be paid the principal of and
              premium, if any, and interest on the Notes as and when the same
              will have become due and payable or
 
       (b) all outstanding notes (except lost, stolen or destroyed notes which
              have been replaced or paid) have been delivered to the trustee for
              cancellation. (Section 401)
 
DEFEASANCE
 
    The indenture will provide that, at the option of NEXTLINK,
 
    (1) if applicable, NEXTLINK will be discharged from any and all obligations
       in respect of the outstanding Notes or
 
    (2) if applicable, NEXTLINK may omit to comply with certain restrictive
       covenants, and that such omission shall not be deemed to be an Event of
       Default under the indenture and the notes, in either case (1) or (2) upon
       irrevocable deposit with the trustee, in trust, of money and/or U.S.
       government obligations which will provide money in an amount sufficient
       in the opinion of a nationally recognized firm of independent certified
       public accountants to pay the principal of and premium, if any, and each
       installment of interest, if any, on the outstanding notes on the Stated
       Maturity. With respect to clause (2), the obligations under the indenture
       other than with respect to such covenants and the Events of Default other
       than the Events of Default relating to such covenants above shall remain
       in full force and effect. Such trust may only be established if, among
       other things
 
       (a) with respect to clause (1), NEXTLINK has received from, or there has
              been published by, the Internal Revenue Service a ruling or there
              has been a change in law after the Issue Date, which in the
              opinion of counsel provides that holders of the notes will not
              recognize gain or loss for Federal income tax purposes as a result
              of such deposit, defeasance and discharge and will be subject to
              Federal income tax on the same
 
                                       81
<PAGE>
              amounts, in the same manner and at the same times as would have
              been the case if such deposit, defeasance and discharge had not
              occurred; or, with respect to clause (2), NEXTLINK has delivered
              to the trustee an opinion of counsel to the effect that the
              holders of the notes will not recognize gain or loss for Federal
              income tax purposes as a result of such deposit and defeasance and
              will be subject to Federal income tax on the same amounts, in the
              same manner and at the same times as would have been the case if
              such deposit and defeasance had not occurred;
 
       (b) no Default or Event of Default shall have occurred or be continuing;
 
       (c) NEXTLINK has delivered to the trustee an opinion of counsel to the
              effect that such deposit shall not cause the trustee or the trust
              so created to be subject to the Investment Company Act of 1940, as
              amended; and
 
       (d) certain other customary conditions precedent are satisfied. (Section
              1201)
 
MODIFICATION AND WAIVER
 
    Modifications and amendments of the indenture may be made by NEXTLINK and
the trustee with the consent of the holders of a majority in aggregate principal
amount of the outstanding notes; PROVIDED, HOWEVER, that no such modification or
amendment may, without the consent of the holder of each outstanding note
affected thereby:
 
    (1) change the due date of the principal of, or any installment of interest
       on, any note;
 
    (2) reduce the principal amount of, or the premium or interest on, any note;
 
    (3) change the place or currency of payment of principal of, or premium or
       interest on, any note;
 
    (4) impair the right to institute suit for the enforcement of any payment on
       or with respect to any note;
 
    (5) reduce the above stated percentage of outstanding notes necessary to
       modify or amend the indenture;
 
    (6) reduce the percentage of aggregate principal amount of outstanding notes
       necessary for waiver of compliance with certain provisions of the
       indenture or for waiver of certain defaults;
 
    (7) modify any provisions of the indenture relating to the modification and
       amendment of the indenture or the waiver of past defaults or covenants,
       except as otherwise specified; or
 
    (8) following the mailing of any Offer to Purchase and until the Expiration
       Date of that Offer to Purchase, modify any Offer to Purchase for the
       notes
 
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<PAGE>
       required under the "Limitation on Asset Dispositions" and the "Change of
       Control" covenants contained in the indenture in a manner materially
       adverse to the holders thereof. (Section 902)
 
    Notwithstanding the foregoing, without the consent of any holder of notes,
NEXTLINK and the trustee may amend or supplement the indenture or the notes
 
    - to cure any ambiguity, defect or inconsistency,
 
    - to provide for uncertificated notes in addition to or in place of
      certificated notes,
 
    - to provide for the assumption of NEXTLINK's obligations to holders of
      notes in the case of a merger or consolidation,
 
    - to make any change that would provide any additional rights or benefits to
      holders of notes or that does not adversely affect the legal rights under
      the indenture of any such holder, or
 
    - to comply with requirements of the commission in order to maintain the
      qualification of the indenture under the Trust Indenture Act. (Section
      901)
 
    The holders of a majority in aggregate principal amount of the outstanding
notes, on behalf of all holders of notes, may waive compliance by NEXTLINK with
certain restrictive provisions of the indenture. (Section 1019) Subject to
certain rights of the trustee, as provided in the indenture, the holders of a
majority in aggregate principal amount of the outstanding notes, on behalf of
all holders of notes, may waive any past default under the indenture, except a
default in the payment of principal, premium or interest or a default arising
from failure to purchase any note tendered pursuant to an Offer to Purchase.
(Section 513)
 
NO PERSONAL LIABILITY OF DIRECTORS, OFFICERS, EMPLOYEES AND STOCKHOLDERS
 
    No director, officer, employee, incorporator or stockholder of NEXTLINK, as
such, shall have any liability for any obligations of NEXTLINK under the notes
or the indenture or for any claim based on, in respect of, or by reason of, such
obligations or their creation. Each holder of notes by accepting a note waives
and releases all such liability. The waiver and release are part of the
consideration for issuance of the notes. Such waiver may not be effective to
waive liabilities under the federal securities laws and it is the view of the
commission that such waiver is against public policy.
 
GOVERNING LAW
 
    The indenture and the notes will be governed by the laws of the State of New
York.
 
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<PAGE>
THE TRUSTEE
 
    The indenture provides that, except during the continuance of an Event of
Default, the trustee will perform only such duties as are specifically set forth
in the indenture. During the existence of an Event of Default, the trustee will
exercise such rights and powers vested in it under the indenture and use the
same degree of care and skill in its exercise as a prudent person would exercise
under the circumstances in the conduct of such person's own affairs. (Section
601)
 
    The indenture and provisions of the Trust Indenture Act incorporated by
reference therein contain limitations on the rights of the trustee, should it
become a creditor of NEXTLINK, to obtain payment of claims in certain cases or
to realize on certain property received by it in respect of any such claim as
security or otherwise. The trustee is permitted to engage in other transactions
with NEXTLINK or any Affiliate, PROVIDED, HOWEVER, that if it acquires any
conflicting interest (as defined in the indenture or in the Trust Indenture
Act), it must eliminate such conflict or resign. (SectionSection 608, 613)
 
                                       84
<PAGE>
                         BOOK-ENTRY; DELIVERY AND FORM
 
    The new notes initially will be represented by one or more permanent global
certificates in definitive, fully registered form. This global note will be
deposited upon issuance with The Depositary Trust Company, New York, New York
and registered in the name of a nominee of the Depository Trust Company.
 
    THE GLOBAL NOTE. We expect that pursuant to procedures established by The
Depository Trust Company
 
    (1) upon the issuance of the global note, The Depository Trust Company or
       its custodian will credit, on its internal system, the principal amount
       of the individual beneficial interests represented by the global note to
       the respective accounts of persons who have accounts with such depositary
       and
 
    (2) ownership of beneficial interests in the global note will be shown on,
       and the transfer of ownership will be effected only through, records
       maintained by The Depository Trust Company or its nominee, with respect
       to interests of participants, and the records of participants, with
       respect to interests of persons other than participants.
 
Ownership of beneficial interests in the global notes will be limited to persons
who have accounts with The Depository Trust Company or persons who hold
interests through participants.
 
    So long as The Depository Trust Company or its nominee is the registered
owner or holder of the new notes, The Depository Trust Company (or the nominee)
will be considered the sole owner or holder of the new notes represented by the
global note for all purposes under the indenture. No beneficial owner of an
interest in the global note will be able to transfer that interest except in
accordance with The Depository Trust Company's procedures.
 
    Payments of interest, principal and other amounts due on the global note
will be made to The Depository Trust Company or its nominee as the registered
owner. None of NEXTLINK, the trustee or any paying agent will have any
responsibility or liability for any aspect of the records relating to or
payments made on account of beneficial ownership interests in the global note or
for maintaining, supervising or reviewing any records relating to this
beneficial ownership interest.
 
    We expect that The Depository Trust Company or its nominee, upon receipt of
any payment of interest, principal or other amounts due on the global note, will
credit participants' accounts with payments in amounts proportionate to their
respective beneficial interests in the global note as shown on the records of
The Depository Trust Company. We also expect that payments by participants to
owners of beneficial interests in the global note held through such participants
will be governed by standing instructions and customary practice, as is the case
with securities held for the accounts of customers registered in the names of
nominees for those customers. These payments will be the responsibility of the
participants.
 
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<PAGE>
    Transfers between participants in The Depository Trust Company will be
effected in the ordinary way through The Depository Trust Company's settlement
system in accordance with The Depository Trust Company rules and will be settled
in same day funds.
 
    The Depository Trust Company has advised us that it will take any action
permitted to be taken by a holder of new notes, including the presentation of
new notes for exchange as described below, only at the direction of a
participant to whose account the The Depository Trust Company interests in the
global note are credited. Further, The Depository Trust Company will take action
only as to such portion of the notes as to which the participant has given such
direction. However, if there is an Event of Default under the indenture, the
Depository Trust Company will exchange the global note for certificated notes,
which it will distribute to its participants.
 
    The Depository Trust Company has advised us as follows: The Depository Trust
Company is a limited purpose trust company organized under the laws of the State
of New York, a member of the Federal Reserve System, a "clearing corporation"
within the meaning of the Uniform Commercial Code and a "Clearing Agency"
registered under to the provisions of Section 17A of the Exchange Act. The
Depository Trust Company was created to hold securities for its participants and
facilitate the clearance and settlement of securities transactions between
participants through electronic book-entry changes in accounts of its
participants, thereby eliminating the need for physical movement of
certificates. Participants include securities brokers and dealers, banks, trust
companies and clearing corporations and certain other organizations. Indirect
access to the Depository Trust Company system is available to others such as
banks, brokers, dealers and trust companies that clear through or maintain a
custodial relationship with a participant, either directly or indirectly.
 
    Although the Depository Trust Company has agreed to the foregoing procedures
in order to facilitate transfers of interests in the global note among
participants of the Depository Trust Company, it is under no obligation to
perform those procedures, and those procedures may be discontinued at any time.
Neither NEXTLINK nor the trustee will have any responsibility of the performance
by the Depository Trust Company or its participants or indirect participants of
their respective obligations under the rules and procedures governing their
operations.
 
    CERTIFICATED SECURITIES. If the Depository Trust Company is at any time
unwilling or unable to continue as a depositary for the global note and a
successor depositary is not appointed by NEXTLINK within 90 days, certificated
notes will be issued in exchange for the global note.
 
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<PAGE>
                      DESCRIPTION OF MATERIAL INDEBTEDNESS
 
DESCRIPTION OF THE 12 1/2% NOTES
 
    GENERAL.  NEXTLINK and NEXTLINK Capital, Inc., (a wholly owned subsidiary of
NEXTLINK) together issued $350 million of 12 1/2% Senior Notes Due April 15,
2006 pursuant to an indenture among NEXTLINK, NEXTLINK Capital and United States
Trust Company of New York, as trustee. On September 6, 1996, NEXTLINK
consummated an offer to exchange these notes for $350 million of 12 1/2% Senior
Notes Due April 15, 2006 that had been registered under the Securities Act.
 
    PRINCIPAL, MATURITY AND INTEREST.  The 12 1/2% Notes are limited in
aggregate principal amount to $350 million and will mature on April 15, 2006.
Interest on the 12 1/2% Notes accrues at 12 1/2% per annum and is payable
semiannually in arrears on April 15 and October 15 of each year. NEXTLINK used
$117.7 million of the net proceeds of the offering of the 12 1/2% notes to
purchase a portfolio of U.S. government securities, to pledge as security for
payment of interest on the 12 1/2% Notes through April 15, 1999 and, under
certain circumstances, as security for repayment of the principal of the 12 1/2%
Notes. Proceeds from the pledged securities may be used by NEXTLINK to make
interest payments on the 12 1/2% Notes through April 15, 1999. The pledged
securities are being held by the trustee pending disbursement.
 
    RANKING.  The 12 1/2% Notes are unsecured senior obligations of the issuers,
will rank equally in right of payment with all existing and future senior
obligations of the issuers and will rank senior in right of payment to all
future subordinated obligations of the issuers.
 
    REDEMPTION.  The 12 1/2% Notes are redeemable at on or after April 15, 2001,
at NEXTLINK's option, in whole or in part, at the following redemption prices
(expressed as percentages of principal amount) plus accrued interest, if
redeemed during the twelve-month period beginning on April 15 of the years
indicated below:
 
<TABLE>
<CAPTION>
YEAR                                                                            PERCENTAGE
- ------------------------------------------------------------------------------  -----------
<S>                                                                             <C>
2001..........................................................................     106.250%
2002..........................................................................     104.167%
2003..........................................................................     102.083%
2004 and thereafter...........................................................     100.000%
</TABLE>
 
    In addition, at any time on or before April 15, 1999, NEXTLINK may redeem up
to 33 1/3% of the original aggregate principal amount of the 12 1/2% Notes with
the net proceeds of a sale of common equity at a redemption price equal to
112.50% of the principal amount thereof, plus accrued and unpaid interest
thereon, if any, to the date of redemption, provided that at least $175 million
of aggregate principal amount of 12 1/2% Notes remains outstanding immediately
after such redemption. Except in connection with a Change of Control or an Asset
Disposition (as defined in the indenture relating to the 12 1/2% Notes) of
NEXTLINK, the issuers are not required to
 
                                       87
<PAGE>
make mandatory redemption or sinking fund payments with respect to the 12 1/2%
Notes.
 
    COVENANTS.  The indenture relating to the 12 1/2% Notes restricts, among
other things, NEXTLINK's ability to incur additional indebtedness, pay dividends
or make certain other restricted payments, incur certain liens to secure debt
which is subordinated to or ranks equally with the 12 1/2% Notes, engage in any
sale and leaseback transaction, sell assign, transfer, lease, convey or
otherwise dispose of substantially all of the assets of NEXTLINK, enter into
certain transactions with affiliates, or incur indebtedness that is subordinate
in right of payment to any senior indebtedness and senior in right of payment to
the 12 1/2% Notes. The indenture relating to the 12 1/2% Notes permits, under
certain circumstances, NEXTLINK's subsidiaries to be deemed unrestricted
subsidiaries and thus not subject to the restrictions of the indenture.
 
    EVENTS OF DEFAULT.  The indenture relating to the 12 1/2% Notes contains
standard events of default, including
 
    - defaults in the payment of principal, premium or interest,
 
    - defaults in the compliance with covenants contained in the indenture,
 
    - cross defaults on more than $10 million of other indebtedness,
 
    - failure to pay more than $10 million of judgments and
 
    - certain events of its subsidiaries.
 
DESCRIPTION OF THE 9 5/8% NOTES
 
    GENERAL.  NEXTLINK issued $400 million of 9 5/8% Senior Notes Due 2007
pursuant to an indenture between NEXTLINK and United States Trust Company of New
York, as trustee. The 9 5/8% Notes have been registered under the Securities
Act.
 
    PRINCIPAL, MATURITY AND INTEREST.  The 9 5/8% Notes are limited in aggregate
principal amount to $400 million and will mature on October 1, 2007. Interest on
the 9 5/8% Notes accrues at 9 5/8% per annum and is payable semiannually in
arrears on April 1 and October 1 of each year.
 
    RANKING.  The 9 5/8% Notes are unsecured senior obligations of NEXTLINK,
will rank equally in right of payment with all existing and future senior
obligations of NEXTLINK and will rank senior in right of payment to all future
subordinated obligations of NEXTLINK.
 
    REDEMPTION.  The 9 5/8% Notes are redeemable on or after October 1, 2002, at
NEXTLINK's option, in whole or in part, at the following redemption prices
 
                                       88
<PAGE>
(expressed as percentages of principal amount) plus accrued interest, if
redeemed during the twelve-month period beginning on October 1 of the years
indicated below:
 
<TABLE>
<CAPTION>
YEAR                                                                            PERCENTAGE
- ------------------------------------------------------------------------------  -----------
<S>                                                                             <C>
2002..........................................................................     104.813%
2003..........................................................................     103.208%
2004..........................................................................     101.604%
2005 and thereafter...........................................................     100.000%
</TABLE>
 
    In addition, at any time on or before October 1, 2002, NEXTLINK may redeem
up to 33 1/3% of the original aggregate principal amount of the 9 5/8% Notes
with the net proceeds of a sale of common equity at a redemption price equal to
109.625% of the principal amount, plus accrued interest, provided that at least
$266.7 million in aggregate principal amount of 9 5/8% Notes remains outstanding
after such redemption. Except in connection with a Change of Control or an Asset
Disposition (as defined in the indenture relating to the 9 5/8% Notes) of
NEXTLINK, NEXTLINK is not required to make mandatory redemption or sinking fund
payments with respect to the 9 5/8% Notes.
 
    COVENANTS.  The indenture relating to the 9 5/8% Notes restricts, among
other things, NEXTLINK's ability to incur additional indebtedness, pay dividends
or make certain other restricted payments, incur certain liens to secure debt
which is subordinated to or ranks equally with the 9 5/8% Notes, engage in any
sale and leaseback transaction, sell assign, transfer, lease, convey or
otherwise dispose of substantially all of the assets of NEXTLINK, enter into
certain transactions with affiliates, or incur indebtedness that is subordinate
in right of payment to any senior indebtedness and senior in right of payment to
the 9 5/8% Notes. The indenture relating to the 9 5/8% Notes permits, under
certain circumstances, NEXTLINK's subsidiaries to be deemed unrestricted
subsidiaries and thus not subject to the restrictions of the indenture.
 
    EVENTS OF DEFAULT.  The indenture relating to the 9 5/8% Notes contains
standard events of default, including
 
    - defaults in the payment of principal, premium or interest,
 
    - defaults in the compliance with covenants contained in the indenture,
 
    - cross defaults on more than $10 million of other indebtedness,
 
    - failure to pay more than $10 million of judgments and
 
    - certain events of its subsidiaries.
 
DESCRIPTION OF THE 9% NOTES
 
    GENERAL.  NEXTLINK issued $335 million of 9% Senior Notes Due 2008 pursuant
to an indenture between NEXTLINK and United States Trust Company of New York, as
trustee. On July 15, 1998, NEXTLINK consummated an offer to
 
                                       89
<PAGE>
exchange such notes for $335 million of 9% Senior Notes Due 2008 that had been
registered under the Securities Act.
 
    PRINCIPAL, MATURITY AND INTEREST.  The 9% Notes are limited in aggregate
principal amount to $335 million and will mature on March 15, 2008. Interest on
the 9% Notes accrues at 9% per annum and is payable semiannually in arrears on
March 15 and September 15 of each year.
 
    RANKING.  The 9% Notes are unsecured senior obligations of NEXTLINK, will
rank equally in right of payment with all existing and future senior obligations
of NEXTLINK and will rank senior in right of payment to all future subordinated
obligations of NEXTLINK.
 
    REDEMPTION.  The 9% Notes are redeemable on or after March 15, 2003, at
NEXTLINK's option, in whole or in part, at the following redemption prices
(expressed as percentages of principal amount) described below plus accrued
interest, if redeemed during the twelve-month period beginning on March 15 of
the years indicated below:
 
<TABLE>
<CAPTION>
YEAR                                                                            PERCENTAGE
- ------------------------------------------------------------------------------  -----------
<S>                                                                             <C>
2003..........................................................................     104.500%
2004..........................................................................     103.000%
2005..........................................................................     101.500%
2006 and thereafter...........................................................     100.000%
</TABLE>
 
    In addition, at any time on or before March 15, 2003, NEXTLINK may redeem up
to 33 1/3% of the original aggregate principal amount of the 9% Notes with the
net proceeds of a sale of common equity at a redemption price equal to 9% of the
principal amount thereof, plus accrued interest, provided that at least 66 2/3%
of the original aggregate principal amount of 9% Notes remains outstanding after
such redemption. Except in connection with a Change of Control or an Asset
Disposition (as defined in the indenture relating to the 9% Notes) of NEXTLINK,
NEXTLINK is not required to make mandatory redemption or sinking fund payments
with respect to the 9% Notes.
 
    COVENANTS.  The indenture relating to the 9% Notes restricts, among other
things, NEXTLINK's ability to incur additional indebtedness, pay dividends or
make certain other restricted payments, incur certain liens to secure debt which
is subordinated to or ranks equally with the 9% Notes, engage in any sale and
leaseback transaction, sell assign, transfer, lease, convey or otherwise dispose
of substantially all of the assets of NEXTLINK, enter into certain transactions
with affiliates, or incur indebtedness that is subordinate in right of payment
to any senior indebtedness and senior in right of payment to the 9% Notes. The
indenture relating to the 9% Notes permits, under certain circumstances,
NEXTLINK's subsidiaries to be deemed unrestricted subsidiaries and thus not
subject to the restrictions of the indenture.
 
                                       90
<PAGE>
    EVENTS OF DEFAULT.  The indenture relating to the 9% Notes contains standard
events of default, including
 
    - defaults in the payment of principal, premium or interest
 
    - defaults in the compliance with covenants contained in the indenture
 
    - cross defaults on more than $10 million of other indebtedness
 
    - failure to pay more than $10 million of judgments and
 
    - certain events of its subsidiaries.
 
DESCRIPTION OF THE 9.45% NOTES
 
    GENERAL.  NEXTLINK issued $636,974,000 principal amount at stated maturity
of 9.45% Senior Discount Notes Due 2008 under an indenture between NEXTLINK and
United States Trust Company of New York, as trustee. On August 24, 1998,
NEXTLINK consummated an offer to exchange such notes for $636,974,000 in
principal amount at stated maturity of 9.45% Senior Discount Notes due 2008 that
have been registered under the Securities Act.
 
    PRINCIPAL, MATURITY AND INTEREST.  The 9.45% Notes are limited to
$636,974,000 aggregate principal amount at stated maturity and will mature on
April 15, 2008. The 9.45% Notes were issued at a discount from their principal
amount to generate aggregate gross of proceeds of approximately $400.0 million.
The 9.45% Notes accrete at a rate of 9.45% compounded semi-annually, to an
aggregate principal amount of $636,974,000 by April 15, 2003. No interest will
accrue on the 9.45% Notes prior to April 15, 2003. The 9.45% Notes bear interest
at 9.45% per annum payable semi-annually on April 15 and October 15 of each
year, commencing October 15, 2003, accruing from April 15, 2003, or from the
most recent interest payment date to which interest has been paid or provided.
 
    RANKING.  The 9.45% Notes are unsecured senior obligations of NEXTLINK, rank
equally in right of payment with all existing and future senior obligations of
NEXTLINK and will rank senior in right of payment to all future subordinated
obligations of NEXTLINK.
 
    REDEMPTION.  The 9.45% Notes are redeemable on or after April 15, 2003, at
NEXTLINK's option, in whole or in part, at the following redemption prices
(expressed as percentages of the principal amount) plus accrued interest, if
redeemed during the 12 month period beginning April 15 of the years indicated:
 
<TABLE>
<CAPTION>
YEAR                                                                            PERCENTAGE
- ------------------------------------------------------------------------------  -----------
<S>                                                                             <C>
2003..........................................................................     104.725%
2004..........................................................................     103.150%
2005..........................................................................     101.575%
2006 and thereafter...........................................................     100.000%
</TABLE>
 
                                       91
<PAGE>
    In addition, at any time on or before April 15, 2003, NEXTLINK may redeem up
to 33 1/3% of the original aggregate principal amount of the 9.45% Notes with
the net proceeds of a sale of common equity, at a redemption price 109.45% of
the principal amount thereof, plus accrued interest, provided that at least
66 2/3% of the original aggregate principal amount of the 9.45% Notes remains
outstanding after such redemption. Except in connection with a Change of Control
or an Asset Disposition (as defined in the indenture relating to the 9.45%
Notes) of NEXTLINK, NEXTLINK is not required to make mandatory redemption or
sinking fund payments with respect to the 9.45% Notes.
 
    COVENANTS.  The indenture relating to the 9.45% Notes restricts, among other
things, NEXTLINK's ability to incur additional indebtedness, pay dividends or
make certain other restricted payments, incur certain liens to secure debt which
is subordinated to or ranks equally with the 9.45% Notes, engage in any sale and
leaseback transaction, sell, assign, transfer, lease, convey or otherwise
dispose of substantially all of the assets of NEXTLINK, enter into certain
transactions with affiliates, or incur indebtedness that is subordinate in right
of payment to any senior indebtedness and senior in right of payment to the
9.45% Notes. The indenture relating to the 9.45% Notes permits, under certain
circumstances, NEXTLINK's subsidiaries to be deemed unrestricted subsidiaries
and thus not subject to the restrictions of such indenture.
 
    EVENTS OF DEFAULT.  The indenture relating to the 9.45% Notes contains
standard events of default, including
 
    - defaults in the payment of principal, premium or interest
 
    - defaults in the compliance with covenants contained in the indenture
 
    - cross defaults on more than $10 million of other indebtedness
 
    - failure to pay more than $10 million of judgments and
 
    - certain events of its subsidiaries.
 
                                       92
<PAGE>
             MATERIAL UNITED STATES FEDERAL INCOME TAX CONSEQUENCES
 
    The following is a summary of United States federal income tax consequences
associated with the ownership and disposition of the notes. Except where noted,
it deals only with notes held as capital assets and does not deal with special
situations, such as those of dealers in securities or currencies, traders in
securities that elect to mark to market, financial institutions, life insurance
companies or tax-exempt organizations. It also does not deal with U.S. holders
whose "functional currency" is not the U.S. dollar or who hold the notes as a
hedge or part of a straddle or conversion transaction. Furthermore, the
discussion below is based upon the provisions of the Internal Revenue Code of
1986, as amended, and regulations, rulings and judicial decisions under the
Internal Revenue Code as of the date of this filing. At any time and without
prior notice, these authorities may be repealed, revoked or modified so as to
result in federal income tax consequences different from those discussed below.
 
    PERSONS CONSIDERING THE TENDER OF THEIR OLD NOTES FOR THE NEW NOTES OFFERED
HEREBY, OR THE PURCHASE, OWNERSHIP OR DISPOSITION OF NOTES, SHOULD CONSULT THEIR
OWN TAX ADVISORS CONCERNING THE FEDERAL INCOME TAX CONSEQUENCES AND CONSEQUENCES
ARISING UNDER THE LAWS OF ANY OTHER TAXING JURISDICTION.
 
THE EXCHANGE OFFER
 
    The exchange of old notes for new notes under the exchange offer should be
treated as a continuation of the corresponding old notes because the terms of
the new notes are substantially the same as the terms of the old notes.
Accordingly, the exchange should not constitute a taxable event to holders and,
therefore:
 
    - no gain or loss should be realized by holders upon receipt of a new note;
 
    - the holding period of the new note should include the holding period of
      the old note; and
 
    - the adjusted tax basis of the new note should be the same as the adjusted
      tax basis of the old note immediately before the exchange.
 
UNITED STATES HOLDERS
 
    A U.S. holder is generally, a citizen or resident of the United States, a
corporation, a partnership or other entity created or organized in or under the
laws of the United States or any political subdivision thereof, or an estate the
income of which is subject to United States federal income taxation regardless
of its source. A trust qualifies as a U.S. holder if a United States court can
exercise primary supervision over the administration of the trust and one or
more United States persons have the authority to control all substantial
decisions of the trust. A U.S. holder is also any other person whose worldwide
income or gain is otherwise subject to United States federal income taxation on
a net income basis.
 
                                       93
<PAGE>
    PAYMENT OF INTEREST
 
    Interest on the notes will be taxable to a U.S. holder as ordinary interest
income in accordance with the U.S. holder's method of tax accounting at the time
that such interest is accrued or actually or constructively received. NEXTLINK
expects that the notes will not be issued with original issue discount for
United States federal income tax purposes.
 
    MARKET DISCOUNT
 
    If a U.S. holder purchases a note for an amount that is less than its issue
price or, in the case of a subsequent purchaser, its principal amount, such U.S.
holder will be treated as having purchased such note at a "market discount,"
unless the amount of such market discount is less than a specified DE MINIMIS
amount. Under the market discount rules, a U.S. holder will be required to treat
any gain on the maturity, sale, exchange, retirement or other disposition of
notes as ordinary income to the extent of the market discount which has not
previously been included in income and is treated as having accrued on such
notes at the time of such disposition. In addition, a U.S. holder may be
required to defer, until the maturity of the notes or earlier disposition in a
taxable transaction, the deduction of all or a portion of the interest expense
on any indebtedness incurred or continued to purchase or carry such notes.
 
    Any market discount will be considered to accrue ratably during the period
from the date of acquisition to the maturity date of the notes, unless the U.S.
holder elects to accrue on a constant yield method. A U.S. holder of notes may
elect to include market discount in income currently as it accrues on either a
ratable or constant yield method, in which case the rule described above
regarding deferral of interest deductions will not apply. This election to
include market discount in income currently, once made, applies to all market
discount obligations acquired on or after the first taxable year to which the
election applies and may not be revoked without the consent of the Internal
Revenue Service. U.S. holders should consult with their own tax advisors
regarding this election.
 
    AMORTIZABLE BOND PREMIUM
 
    A U.S. holder that purchases notes for an amount greater than the principal
amount of the notes will be considered to have purchased such notes with "bond
premium." A U.S. holder generally may elect to amortize the bond premium over
the remaining term of the notes on a constant yield method. The amount amortized
in any year will be treated as a reduction of the U.S. holder's interest income
from the notes. Bond premium on a note held by a U.S. holder that does not make
such an election will decrease the gain or increase the loss otherwise
recognized on disposition of the notes. Any election to amortize bond premium
applies to all debt obligations, other than debt obligations the interest on
which is excludable from gross income: held by the U.S. holder at the beginning
of the first taxable year to which the election applies or thereafter acquired
by the U.S. holder, and may not be revoked without the
 
                                       94
<PAGE>
consent of the Internal Revenue Service. U.S. holders should consult with their
tax advisors regarding this election.
 
    SALE, EXCHANGE AND RETIREMENT OF NOTES
 
    A U.S. holder's adjusted tax basis in notes will, in general, equal the
holder's cost therefor increased by any market discount included in the U.S.
holder's income and reduced by any amortized bond premium. Upon the sale,
exchange or retirement of notes, a U.S. holder will recognize gain or loss equal
to the difference between the amount realized upon the sale, exchange or
retirement and the U.S. holder's adjusted tax basis in the notes. Except with
respect to market discount accrued and unpaid interest, such gain or loss will
be capital gain or loss. Long-term capital gain of an individual U.S. holder is
generally subject to a maximum tax rate of 20% in respect of property held for
more than twelve months. The deductibility of capital losses is subject to
limitations.
 
    EXCHANGE OFFER
 
    The exchange of notes for new notes pursuant to the exchange offer should
not be taxable to the holders of the notes. Any additional interest payment due
to the holders of the notes will be taxable income and may be characterized as
additional interest income for tax purposes.
 
NON-UNITED STATES HOLDERS
 
    For purposes of this discussion, a non-U.S. holder is any holder of a note
who is a nonresident alien individual or a foreign corporation, partnership or
estate or trust which is not subject to United States federal income tax on a
net income basis in respect of income or gain from a note.
 
    Under present United States federal income and estate tax law, and subject
to the discussion of backup withholding below:
 
        (1) payments of principal, premium, if any, and interest by NEXTLINK or
    any of its paying agents to a non-U.S. holder will not be subject to United
    States federal withholding tax if, in the case of interest,
 
           (a) the beneficial owner of the note does not actually or
       constructively own 10% or more of the total combined voting power of all
       classes of stock of NEXTLINK,
 
           (b) the beneficial owner of the note is not a controlled foreign
       corporation that is related to NEXTLINK through stock ownership, and
 
           (c) either:
 
                  (A) the beneficial owner of the note certifies to NEXTLINK or
              its agent, under penalties of perjury, that it is not a U.S.
              holder and provides its name and address; or
 
                                       95
<PAGE>
                  (B) a securities clearing organization, bank or other
              financial institution that holds customers' securities in the
              ordinary course of its trade or business and holds the note
              certifies to NEXTLINK or its agent under penalties of perjury that
              this statement has been received from the beneficial owner by it
              or by a one of the financial institutions between it and the
              beneficial owner and furnishes the payor with a copy thereof;
 
        (2) a non-U.S. holder of a note will not be subject to United States
    federal withholding tax on any gain realized on the sale or exchange of a
    note; and
 
        (3) a note held by an individual who at death is not a citizen or
    resident of the United States will not be includible in the individual's
    gross estate for purposes of the United States federal estate tax as a
    result of the individual's death if
 
           (a) the individual did not actually or constructively own 10% or more
       of the total combined voting power of all classes of stock in NEXTLINK,
       and
 
           (b) the income on the note would not have been effectively connected
       with a United States trade or business of the individual at the
       individual's death.
 
    Recently finalized regulations, that are generally effective with respect to
payments made after December 31, 1999, would provide alternative methods for
satisfying the certification requirement described in clause (1)(c) above. These
regulations also require, in the case of notes held by a foreign partnership,
that (x) the certification described in clause (1)(c) above would generally be
applied to the partners of the partnership and (y) the partnership provide
certain information, including a United States taxpayer identification number. A
look-through rule will apply in the case of tiered partnerships. Non-U.S.
holders who exchange their old notes for new notes under the exchange offer are
urged to consult their tax advisor regarding the regulations described above.
 
BACKUP WITHHOLDING AND INFORMATION REPORTING
 
    UNITED STATES HOLDERS
 
    In general, information reporting requirements will apply to some payments
of principal, premium, if any, and interest and to the proceeds of sale of a
note made to holders other than recipients which are specifically exempt, such
as corporations. Backup withholding and information reporting generally will not
apply to payments of principal, premium, if any, and interest on notes made
outside the United States by NEXTLINK or any paying agent to a holder. However,
a 31% backup withholding tax will apply to payments made to an address in the
United States or by transfer to an account maintained by the holder with a bank
in the United States. This backup withholding tax may also apply to some of the
payments described above if the U.S. holder fails to provide a taxpayer
identification number or certification of foreign or
 
                                       96
<PAGE>
other exempt status or if the U.S. holder is notified by the Internal Revenue
Service that it has failed to report in full dividend and interest income.
 
    NON-UNITED STATES HOLDERS
 
    Under current law, information reporting on Internal Revenue Service Form
1099 and backup withholding will not apply to payments of principal, premium, if
any and interest made by NEXTLINK or a paying agent to a non-U.S. holder on a
note; so long as the certification described in clause (1)(c) under "Non-United
States Holders" above is received and the payor does not have actual knowledge
that the holder is a United States person. NEXTLINK or a paying agent, however,
may report (on Internal Revenue Service Form 1042S) payments of interest on
notes.
 
    Payments of the proceeds from the sale by a non-U.S. holder of a note made
to or through a foreign office of a broker will not be subject to information
reporting or backup withholding. Information reporting requirements will apply,
however, if the broker is a United States person, a controlled foreign
corporation for United States tax purposes or a foreign person 50% or more of
whose gross income is effectively connected with a United States trade or
business for a specified three-year period. Payments of the proceeds from the
sale of a note to or through the United States office of a broker is subject to
information reporting and backup withholding unless the holder or beneficial
owner certifies as to its non-United States status or otherwise establishes an
exemption from information reporting and backup withholding. See the discussion
above with respect to the rules under the final withholding regulations.
 
                              PLAN OF DISTRIBUTION
 
    Each holder desiring to participate in the exchange offer will be required
to represent, among other things, that
 
        (1) it is not an "affiliate" (as defined in Rule 405 of the Securities
    Act) of NEXTLINK,
 
        (2) it is not engaged in, and does not intend to engage in, and has no
    arrangement or understanding with any person to participate in, a
    distribution of the new notes, and
 
        (3) it is acquiring the new notes in the ordinary course of its
    business.
 
A holder unable to make the above representations is referred to as a restricted
holder. A restricted holder will not be able to participate in the exchange
offer, and may only sell its old notes pursuant to a registration statement
containing the selling securityholder information required by Item 507 of
Regulation S-K of the Securities Act, or pursuant to an exemption from the
registration requirement of the Securities Act.
 
    Each participating broker-dealer is required to acknowledge in the letter of
transmittal that it acquired the old notes as a result of market-making
activities or
 
                                       97
<PAGE>
other trading activities and that it will deliver a prospectus in connection
with the resale of such new notes. Based upon interpretations by the staff of
the Securities and Exchange Commission, NEXTLINK believes that new notes issued
pursuant to the exchange offer to participating broker-dealers may be offered
for resale, resold, and otherwise transferred by a participating broker-dealer
upon compliance with the prospectus delivery requirements, but without
compliance with the registration requirements, of the Securities Act. NEXTLINK
has agreed that for a period of 30 days following consummation of the exchange
offer, they will make this prospectus available to participating broker-dealers
for use in connection with any such resale. During such period of time, delivery
of this prospectus, as it may be amended or supplemented, will satisfy the
prospectus delivery requirements of a participating broker-dealer engaged in
market making or other trading activities.
 
    Based upon interpretations by the staff of the Securities and Exchange
Commission, NEXTLINK believes that new notes issued pursuant to the exchange
offer may be offered for resale, resold and otherwise transferred by their
holder, other than a participating broker-dealer, without compliance with the
registration and prospectus delivery requirements of the Securities Act.
 
    NEXTLINK will not receive any proceeds from any sale of new notes by broker-
dealers. new notes received by participating broker-dealers for their own
account pursuant to the exchange offer may be sold from time to time in one or
more transactions in the over-the-counter market, in negotiated transactions,
through the writing of options on the new notes or a combination of such methods
of resale, at market prices prevailing at the time of resale, at prices related
to such prevailing market prices or at negotiated prices. Any such resale may be
made directly to purchasers or to or through brokers or dealers who may receive
compensation in the form of commissions or concessions from any such
participating broker-dealer and/or the purchasers of any such new notes. Any
participating broker-dealer that resells new notes that were received by it for
its own account pursuant to the exchange offer and any broker or dealer that
participates in a distribution of such new notes may be deemed to be an
"underwriter" within the meaning of the Securities Act and any profit on any
such resale of new notes and any commissions or concessions received by any such
persons may be deemed to be underwriting compensation under the Securities Act.
The letter of transmittal states that by acknowledging that it will deliver and
by delivering a prospectus, a participating broker-dealer will not be deemed to
admit that it is an "underwriter" within the meaning of the Securities Act.
 
    NEXTLINK has agreed to pay all expenses incidental to the exchange offer
other than commissions and concessions of any brokers or dealers and will
indemnify holders of the notes, including any broker-dealers, against certain
liabilities, including liabilities under the Securities Act, as set forth in the
registration rights agreement.
 
                                       98
<PAGE>
                INCORPORATION OF MATERIAL DOCUMENTS BY REFERENCE
 
    The Securities and Exchange Commission allows us to "incorporate by
reference" the information we file with them, which means we can disclose
important information to you by referring you to those documents. The
information included in the following documents is incorporated by reference and
is considered to be a part of this prospectus. The most recent information that
we file with the Securities and Exchange Commission automatically updates and
supersedes more dated information. We have previously filed the following
document with the Securities and Exchange Commission and are incorporating it by
reference into this prospectus:
 
        Our Annual Report on Form 10-K for the fiscal year ended December 31,
    1998, filed on March 29, 1999;
 
    We also incorporate by reference all documents subsequently filed by us
pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act until all of
the old notes are exchanged for new notes.
 
    We will provide without charge to each person, including any person having a
control relationship with that person, to whom a prospectus is delivered, a copy
of any or all of the information that has been incorporated by reference in this
prospectus but not delivered with this prospectus. If you would like to obtain
this information from us, please direct your request, either in writing or by
telephone to R. Bruce Easter, Jr., General Counsel and Secretary, NEXTLINK
Communications, Inc., 500 108(th) Avenue N.E., Suite 2200, Bellevue, Washington
98004. In order to insure timely delivery of the documents, any request should
be made five days before March   , 1999, which is when the exchange offer
expires.
 
                                 LEGAL MATTERS
 
    The validity of the new notes will be passed upon for NEXTLINK by Willkie
Farr & Gallagher, New York, New York.
 
                                    EXPERTS
 
    The audited financial statements included in the NEXTLINK's Annual Report on
Form 10-K, filed on March 29, 1999, which is incorporated herein by reference,
have been audited by Arthur Andersen LLP, independent public accountants, as
indicated in their report with respect thereto, and are included herein in
reliance upon the authority of said firm as experts in giving said reports.
 
                                       99
<PAGE>
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                                  $500,000,000
 
                               OFFER TO EXCHANGE
                         10 3/4% SENIOR NOTES DUE 2008
                           THAT HAVE BEEN REGISTERED
                UNDER THE SECURITIES ACT OF 1933 FOR OUTSTANDING
                         10 3/4% SENIOR NOTES DUE 2008
 
                             ---------------------
 
                              P R O S P E C T U S
 
                              DATED APRIL 1, 1999
                             ---------------------
 
                                     [LOGO]
 
                                    NEXTLINK
                              COMMUNICATIONS, INC.
 
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