<PAGE>
                                                                    EXHIBIT 10.4



                            REGISTRATION RIGHTS AGREEMENT


         THIS REGISTRATION RIGHTS AGREEMENT, dated as of January 15, 1997,
is between NEXTLINK COMMUNICATIONS, INC., a Washington corporation (the
"Company") and the parties that are signatories to this Agreement that are
holders of Class B Common Stock of the Company or of options to purchase Class B
Common Stock (the "Holders").

         WHEREAS, the Holders have made capital contributions to NEXTLINK
Communications, L.L.C., a Washington limited liability company ("LLC"), the
predecessor in interest to the Company, and currently own all of the issued and
outstanding shares of Class B common stock, $.01 par value, of the Company, or
options to purchase the Class B Common stock, (the "Class B Common Stock"); and 

         WHEREAS, in connection with the incorporation of the Company, the
Company wishes to grant to the Holders certain registration rights with respect
to the shares of Class A common stock, par value $.01 per share of the Company
(the "Class A Common Stock") for which the shares of Class B Common Stock are
convertible that the Holders currently own or may acquire in the future, as
provided further herein. 

         NOW THEREFORE, in consideration of the capital contributions made by
the Holders to LLC and of the promises herein contained, the parties hereto
agree as follows:

         1.   DEFINITIONS.

         As used in this Agreement:

         (i)  the terms "register," "registered" and "registration" refer to a
registration effected by preparing and filing a registration statement in
compliance with the Act (and any post-effective amendments filed or required to
be filed) and the declaration or ordering of effectiveness of such registration
statement;

         (ii)  the term "Registrable Securities" means (A) all shares of Class
A Common Stock owned by the Holders as of the date hereof, (B) any shares of
Class A Common Stock acquired by the Holders through conversion of Class B
Common Stock or otherwise and (C) any capital stock of the Company issued as a
dividend or other distribution with respect to, or in exchange for or in
replacement of, the shares of Class A Common Stock referred to in clause (A) or
(B) above;

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         (iii)  the term "Holder" shall mean solely those parties that are a
signatory to this Agreement;

         (iv)  the term "Initiating Holders" shall mean any Holder or Holders
who in the aggregate are Holders of more than 4% of the then outstanding
Registrable Securities;

         (v)  "Commission" shall mean the Securities and Exchange Commission or
any other federal agency at the time administering the Act;

         (vi)  "Qualifying IPO" shall mean a public offering of Class A Common
Stock of the Company that results in net proceeds to the Company of not less
than Seventy Five Million Dollars ($75,000,000) or such lesser amount as the
Directors of the Company may, in their discretion, determine to be adequate to
commence the rights of the Holders hereunder;

         (vii)  "Registration Expenses" shall mean all third-party expenses
incurred by the Company in compliance with Sections 2 and 3 hereof, including,
without limitation, all registration and filing fees, printing expenses, fees
and disbursements of counsel for the Company and the underwriters, if any, blue
sky fees and expenses and the third-party expenses of any special audits
incident to or required by any such registration (but excluding the compensation
of regular employees of the Company, which shall be paid in any event by the
Company);

         (viii)  "Selling Expenses" shall mean all underwriting discounts and
selling commissions applicable to the sale of Registrable Securities and all
fees and disbursements of counsel for each of the Holders;

         (ix)  "Act" shall mean the Securities Act of 1933, as amended; and

         (x)  "Exchange Act" shall mean the Securities Exchange Act of 1934.

         2.  REQUESTED REGISTRATION.

         (i)  REQUEST FOR REGISTRATION.  If the Company shall receive from an
Initiating Holder, at any time after a Qualifying IPO, a written request that
the Company effect any registration with respect to all or a part of the
Registrable Securities, the Company will:

              (A) promptly give written notice of the proposed registration,
    qualification or compliance to all other Holders; and

              (B) as soon as practicable, use its diligent best efforts to
    effect such registration (including, without limitation, the execution of
    an undertaking to file post-effective amendments, appropriate qualification
    under applicable blue sky or other 

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    state securities laws and appropriate compliance with applicable
    regulations issued under the Act) as may be so requested and as would
    permit or facilitate the sale and distribution as soon as is
    practicable of all or such portion of such Registrable Securities as
    are specified in such request, together with all or such portion of
    the Registrable Securities of any Holder or Holders joining in such
    request as are specified in a written request received by the Company
    within twenty (20) business days after written notice from the Company
    is given under Section 2(i)(A) above; PROVIDED that the Company shall
    not be obligated to effect, or take any action to effect, any such
    registration pursuant to this Section 2:

              (a)  In any particular jurisdiction in which the Company would be
         required to execute a general consent to service of process in
         effecting such registration, qualification or compliance, unless the
         Company is already subject to service in such jurisdiction and except
         as may be required by the Act or applicable rules or regulations
         thereunder;

              (b)  After the Company has effected a total of two (2) such
         registrations pursuant to this Section 2 and such registrations have
         been declared or ordered effective and the sales of such Registrable
         Securities shall have closed; or

              (c)  If the Registrable Securities requested by all Holders to be
         registered pursuant to such request do not have an anticipated
         aggregate public offering price (before any underwriting discounts and
         commissions) of not less than $10,000,000.

         The registration statement filed pursuant to the request of the
Initiating Holders may, subject to the provisions of Section 2(ii) below,
include other securities of the Company which are held by officers or directors
of the Company, or which are held by persons who, by virtue of agreements with
the Company, are entitled to include their securities in any such registration,
but the Company shall have no absolute right to include any of its securities in
any such registration.

         The registration rights set forth in this Section 2 are personal to
the Holders and shall not be assignable, by operation of law or otherwise.

         (ii)  UNDERWRITING.  If the Initiating Holders intend to distribute
the Registrable Securities covered by their request by means of an underwriting,
they shall so advise the Company as a part of their request made pursuant to
Section 2.

         If officers or directors of the Company holding other securities of
the Company shall request inclusion in any registration pursuant to Section 2,
or if holders of securities of the Company other than Registrable Securities who
are entitled, by contract with the Company 

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or otherwise, to have securities included in such a registration (the "Other
Stockholders") request such inclusion, the Holders shall offer to include the
securities of such officers, directors and Other Stockholders in the
underwriting and may condition such offer on their acceptance of the further
applicable provisions of this Section 2.  The Holders whose shares are to be
included in such registration and the Company shall (together with all officers,
directors and Other Stockholders proposing to distribute their securities
through such underwriting) enter into an underwriting agreement in customary
form with the representative of the underwriter or underwriters selected for
such underwriting by the Initiating Holders and reasonably acceptable to the
Company.  Notwithstanding any other provision of this Section 2, if the
representative advises the Holders that marketing factors require a limitation
on the number of shares to be underwritten, the securities of the Company held
by officers or directors of the Company and the securities held by Other
Stockholders shall be excluded from such registration to the extent so required
by such limitation.  If, after the exclusion of such shares, further reductions
are still required, the number of shares included in the registration by each
Holder shall be reduced on a pro rata basis (based on the number of shares
proposed to be sold by such Holder), by such minimum number of shares as is
necessary to comply with such request.  No Registrable Securities or any other
securities excluded from the underwriting by reason of the underwriter's
marketing limitation shall be included in such registration.  If any officer,
director or Other Stockholder who has requested inclusion in such registration
as provided above disapproves of the terms of the underwriting, such person may
elect to withdraw therefrom by written notice to the Company, the underwriter
and the Initiating Holders.  The securities so withdrawn shall also be withdrawn
from registration.  If the underwriter has not limited the number of Registrable
Securities or other securities to be underwritten, the Company may include its
securities for its own account in such registration if the representative so
agrees and if the number of Registrable Securities and other securities which
would otherwise have been included in such registration and underwriting will
not thereby be limited.

         (iii)  Notwithstanding the foregoing, if the Company shall furnish to
Holders requesting the filing of a registration statement pursuant to Section
2(i), a certificate signed by the President or Chief Executive Officer of the
Company stating that in the good faith judgment of the Board of Directors of the
Company, it would be seriously detrimental to the Company and its shareholders
for such registration statement to be filed and it is therefore essential to
defer the filing of such registration statement, then the Company shall have the
right to defer such filing for a period of not more than 120 days after receipt
of the request of the Initiating Holders; PROVIDED, HOWEVER, that the Company
may not utilize this right more than once in any twelve (12) month period.

         3.  COMPANY REGISTRATION.

         (i)  If, at any time after a Qualifying IPO, the Company shall
determine to register any of its equity securities either for its own account or
for the account of a security 

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holder or holders exercising their respective demand registration rights, other
than a registration relating solely to employee benefit plans, or a registration
relating solely to a Commission Rule 145 transaction, or a registration on any
registration form which does not permit secondary sales or does not include
substantially the same information as would be required to be included in a
registration statement covering the sale of Registrable Securities, the Company
will:

              (A) promptly give to each of the Holders a written notice thereof
    (which shall include a list of the jurisdictions in which the Company
    intends to attempt to qualify such securities under the applicable blue sky
    or other state securities laws); and

              (B) include in such registration (and any related qualification
    under blue sky laws or other compliance), and in any underwriting involved
    therein, all the Registrable Securities specified in a written request or
    requests, made by the Holders within twenty (20) days after receipt of the
    written notice from the Company described in clause (i) above, except as
    set forth in Section 3(ii) below.  Such written request may specify all or
    a part of the Holders' Registrable Securities.

         (ii)  UNDERWRITING.  If the registration of which the Company gives
notice is for a registered public offering involving an underwriting, the
Company shall so advise each of the Holders as a part of the written notice
given pursuant to Section 3(i)(A).  In such event, the right of each of the
Holders to registration pursuant to this Section 3 shall be conditioned upon
such Holders' participation in such underwriting and the inclusion of such
Holders' Registrable Securities in the underwriting to the extent provided
herein.  The Holders whose shares are to be included in such registration shall
(together with the Company and the Other Stockholders distributing their
securities through such underwriting) enter into an underwriting agreement in
customary form with the representative of the underwriter or underwriters
selected for underwriting by the Company.  Notwithstanding any other provision
of this Section 3, if the representative determines that marketing factors
require a limitation on the number of shares to be underwritten, the
representative may (subject to the allocation priority set forth below) limit
the number of Registrable Securities to be included in the registration and
underwriting.  The Company shall so advise all holders of securities requesting
registration, and the number of shares of securities that are entitled to be
included in the registration and underwriting shall be allocated in the
following manner:  The securities of the Company held by officers, directors and
Other Stockholders of the Company (other than securities held by holders who by
contractual right initiated the demand for such registration ("Demanding
Holders")) shall be excluded from such registration and underwriting to the
extent required by such limitation, and, if a limitation on the number of shares
is still required, the number of shares that may be included in the registration
and underwriting by each of the Holders and Demanding Holders shall be reduced,
on a pro rata basis (based on the number of shares proposed to be sold by such
Holder or Demanding Holder), by such minimum number of shares as is necessary to
comply with such limitation.  If any of the Holders or Demanding Holders 


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<PAGE>

or any officer, director or Other Stockholder disapproves of the terms of any
such underwriting, he may elect to withdraw therefrom by written notice to the
Company and the underwriter.  Any Registrable Securities or other securities
excluded or withdrawn from such underwriting shall be withdrawn from such
registration.

         (iii)  NUMBER AND TRANSFERABILITY.  Each of the Holders shall be
entitled to have its shares included in an unlimited number of registrations
pursuant to this Section 3.  The registration rights granted pursuant to this
Section 3 are personal to the Holders and shall not be assignable, by operation
of law or otherwise.

         4.  EXPENSES OF REGISTRATION.  All Registration Expenses and Selling
Expenses incurred in connection with any registration, qualification or
compliance pursuant to Section 2 of this Agreement shall be borne by the holders
of the securities so registered pro rata on the basis of the number of shares so
registered.  Without limiting the generality of the foregoing, in the event the
Company includes shares in any registration, qualification or compliance
pursuant to Section 2 of this Agreement, the Company shall pay the Registration
Expenses in proportion to the Company's share of the total number of shares
included in such registration.  All Registration Expenses incurred in connection
with any registration, qualification or compliance pursuant to Section 3 of this
Agreement shall be borne by the Company (or the Demanding Holders if so provided
in the applicable contract), and all Selling Expenses incurred in connection
with any such registration, qualification or compliance shall be borne by the
Holders of securities so registered pro rata on the basis of the number of
shares so registered.

         5.  REGISTRATION PROCEDURES.  In the case of each registration
effected by the Company pursuant to this Agreement, the Company will keep the
Holders, as applicable, advised in writing as to the initiation of each
registration and as to the completion thereof.  The Company will:

              (i)  Keep such registration effective for a period of one hundred
    eighty (180) days or until the Holders, as applicable, have completed the
    distribution described in the registration statement relating thereto,
    whichever first occurs; provided, however, that (A) such 180-day period
    shall be extended for a period of time equal to the period during which the
    Holders, as applicable, refrain from selling any securities included in
    such registration in accordance with provisions in Section 9 hereof; and
    (B) in the case of any registration of Registrable Securities on Form S-3
    which are intended to be offered on a continuous or delayed basis, such
    180-day period shall be extended until all such Registrable Securities are
    sold, provided that Rule 415, or any successor rule under the Act, permits
    an offering on a continuous or delayed basis, and provided further that
    applicable rules under the Act governing the obligation to file a
    post-effective amendment permit, in lieu of filing a post-effective
    amendment which (1) includes any prospectus required by Section 10(a) of
    the Act or (2) reflects facts or 

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    events representing a material or fundamental change in the
    information set forth in the registration statement, the incorporation
    by reference of information required to be included in (1) and (2)
    above to be contained in periodic reports filed pursuant to Section 12
    or 15(d) of the Exchange Act in the registration statement.

              (ii)  Furnish such number of prospectuses and other documents
    incident thereto as each of the Holders, as applicable, from time to time
    may reasonably request; PROVIDED, HOWEVER, that the Holders, pro rata on
    the basis of the number of their shares so included in such registration,
    reimburse the Company for expenses incurred in performing its obligations
    under this Section 5.  

              (iii)     Prepare and file with the SEC such amendments and
    supplements to such registration statement and the prospectus used in
    connection with such registration statement as may be necessary to comply
    with the provisions of the Act with respect to the disposition of all
    securities covered by such registration statement.  

              (iv) Use its best efforts to register and qualify the securities
    covered by such registration statement under such other securities or Blue
    Sky laws of such jurisdictions as shall be reasonably requested by the
    Holders, provided that the Company shall not be required in connection
    therewith or as a condition thereto to qualify to do business or to file a
    general consent to service of process in any such states or jurisdictions.  

              (v)  In the event of any underwritten public offering, enter into
    and perform its obligations under an underwriting agreement, in usual and
    customary form, with the managing underwriter of such offering.  Each
    Holder participating in such underwriting shall also enter into and perform
    its obligations under such an agreement.

              (vii)     Furnish, at the request of any Holder requesting
    registration of Registrable Securities pursuant to this Agreement, on the
    date that such Registrable Securities are delivered to the underwriters for
    sale in connection with a registration pursuant to this Agreement, if such
    securities are being sold through underwriters, or, if such securities are
    not being sold through underwriters, on the date that the registration
    statement with respect to such securities becomes effective, (A) an
    opinion, dated such date, of the counsel representing the Company for the
    purposes of such registration, in form and substance as is customarily
    given to underwriters in an underwritten public offering, addressed to the
    underwriters, if any, and to the Holders requesting registration of
    Registrable Securities and (B) a letter dated such date, from the
    independent certified public accountants of the Company, in form and
    substance as is customarily given by independent certified public
    accountants to underwriters in 

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    an underwritten public offering, addressed to the underwriters, if
    any, and to the Holders requesting registration of Registrable
    Securities.  

         6.  INDEMNIFICATION.

         (i)  The Company will indemnify each of the Holders, as applicable,
each of its officers, directors and partners, and each person controlling each
of the Holders, with respect to each registration which has been effected
pursuant to this Agreement, and each underwriter, if any, and each person who
controls any underwriter, against all claims, losses, damages and liabilities
(or actions in respect thereof) arising out of or based on any untrue statement
(or alleged untrue statement) of a material fact contained in any prospectus,
offering circular or other document (including any related registration
statement, notification or the like) incident to any such registration,
qualification or compliance, or based on any omission (or alleged omission) to
state therein a material fact required to be stated therein or necessary to make
the statements therein not misleading, or any violation by the Company of the
Act or any rule or regulation thereunder applicable to the Company and relating
to action or inaction required of the Company in connection with any such
registration, qualification or compliance, and will reimburse each of the
Holders, each of its officers, directors and partners, and each person
controlling each of the Holders, each such underwriter and each person who
controls any such underwriter, for any legal and any other expenses reasonably
incurred in connection with investigating and defending any such claim, loss,
damage, liability or action, provided that the Company will not be liable in any
such case to the extent that any such claim, loss, damage, liability or expense
arises out of or is based on any untrue statement or omission based upon written
information furnished to the Company by the Holders or underwriter and stated to
be specifically for use therein.

         (ii)  Each of the Holders will, if Registrable Securities held by it
are included in the securities as to which such registration, qualification or
compliance is being effected, indemnify the Company, each of its directors and
officers and each underwriter, if any, of the Company's securities covered by
such a registration statement, each person who controls the Company or such
underwriter within the meaning of the Act and the rules and regulations
thereunder, each Other Stockholder and each of their officers, directors, and
partners, and each person controlling such Other Stockholder against all claims,
losses, damages and liabilities (or actions in respect thereof) arising out of
or based on any untrue statement (or alleged untrue statement) of a material
fact contained in any such registration statement, prospectus, offering circular
or other document made by such Holder, or any omission (or alleged omission) to
state therein a material fact required to be stated therein or necessary to make
the statements by such Holder therein not misleading, and will reimburse the
Company and such Other Stockholders, directors, officers, partners, persons,
underwriters or control persons for any legal or any other expenses reasonably
incurred in connection with investigating or defending any such claim, loss,
damage, liability or action, in each case to the extent, but only to the extent,
that such untrue statement (or alleged untrue statement) or 

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omission (or alleged omission) is made in such registration statement,
prospectus, offering circular or other document in reliance upon and in
conformity with written information furnished to the Company by such Holder and
stated to be specifically for use therein; provided, however, that the
obligations of each of the Holders hereunder shall be limited to an amount equal
to the net proceeds to such Holder of securities sold as contemplated herein.

         (iii)  Each party entitled to indemnification under this Section 6
(the "Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the Indemnifying Party to assume the defense of any such claim or any
litigation resulting therefrom; provided that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or any litigation resulting
therefrom, shall be approved by the Indemnified Party (whose approval shall not
unreasonably be withheld) and the Indemnified Party may participate in such
defense at such party's expense (unless the Indemnified Party shall have
reasonably concluded that there may be a conflict of interest between the
Indemnifying Party and the Indemnified Party in such action, in which case the
fees and expenses of counsel shall be at the expense of the Indemnifying Party),
and provided further that the failure of any Indemnified Party to give notice as
provided herein shall not relieve the Indemnifying Party of its obligations
under this Section 6 unless the Indemnifying Party is materially prejudiced
thereby.  No Indemnifying Party, in the defense of any such claim or litigation,
shall, except with the consent of each Indemnified Party, consent to entry of
any judgment or enter into any settlement which does not include as an
unconditional term thereof the giving by the claimant or plaintiff to such
Indemnified Party of a release from all liability in respect to such claim or
litigation.  Each Indemnified Party shall furnish such information regarding
itself or the claim in question as an Indemnifying Party may reasonably request
in writing and as shall be reasonably required in connection with the defense of
such claim and litigation resulting therefrom.

         (iv) If the indemnification provided for in this Section 6 is held by
a court of competent jurisdiction to be unavailable to an Indemnified Party with
respect to any loss, liability, claim, damage or expense referred to herein,
then the Indemnifying Party, in lieu of indemnifying such Indemnified Party
hereunder, shall contribute to the amount paid or payable by such Indemnified
Party as a result of such loss, liability, claim, damage or expense in such
proportion as is appropriate to reflect the relative fault of the Indemnifying
Party on the one hand and of the Indemnified Party on the other in connection
with the statements or omissions which resulted in such loss, liability, claim,
damage or expense, as well as any other relevant equitable considerations.  The
relative fault of the Indemnifying Party and of the Indemnified Party shall be
determined by reference to, among other things, whether the untrue or alleged
untrue statement of a material fact or the omission to state a material fact
relates to information supplied by the Indemnifying Party or by the Indemnified
Party and the parties' relative intent, knowledge, access to information and
opportunity to correct or prevent such statement or omission.

                                          9


<PAGE>

         (v) Notwithstanding the foregoing, to the extent that the provisions
on indemnification and contribution contained in the underwriting agreement
entered into in connection with any underwritten public offering contemplated by
this Agreement are in conflict with the foregoing provisions, the provisions in
such underwriting agreement shall be controlling.

         (vi) The foregoing indemnity agreement of the Company and Holders is
subject to the condition that, insofar as they relate to any loss, claim,
liability or damage made in a preliminary prospectus but eliminated or remedied
in the amended prospectus on file with the Commission at the time the
registration statement in question becomes effective or the amended prospectus
filed with the Commission pursuant to Commission Rule 424(b) (the "Final
Prospectus"), such indemnity agreement shall not inure to the benefit of any
underwriter if a copy of the Final Prospectus was furnished to the underwriter
and was not furnished to the person asserting the loss, liability, claim or
damage at or prior to the time such action is required by the Act.

         7.  INFORMATION BY THE HOLDERS.  Each of the Holders and each Other
Stockholder holding securities included in any registration, shall furnish to
the Company such information regarding such Holder or Other Stockholder and the
distribution proposed by such Holder or Other Stockholder as the Company may
reasonably request in writing and as shall be reasonably required in connection
with any registration, qualification or compliance referred to in this
Agreement.

         8.  RULE 144 REPORTING.

         With a view to making available the benefits of certain rules and
regulations of the Commission which may permit the sale of restricted securities
to the public without registration, the Company agrees to:

              (i)  make and keep public information available as those terms
    are understood and defined in Rule 144, at all times from and after ninety
    (90) days following the effective date of the first registration under the
    Act filed by the Company for an offering of its securities to the general
    public;

              (ii)  use its best efforts to file with the Commission in a
    timely manner all reports and other documents required of the Company under
    the Act and the Exchange Act at any time after it has become subject to
    such reporting requirements; and

              (iii)  so long as the Holder owns any Registrable Securities,
    furnish to the Holder upon request, a written statement by the Company as
    to its compliance with the reporting requirements of Rule 144 (at any time
    from and after ninety (90) days 

                                          10


<PAGE>

    following the effective date of the first registration statement filed
    by the Company for an offering of its securities to the general
    public), and of the Act and the Exchange Act (at any time after it has
    become subject to such reporting requirements), a copy of the most
    recent annual or quarterly report of the Company, and such other
    reports and documents so filed as the Holder may reasonably request in
    availing itself of any rule or regulation of the Commission allowing
    the Holder to sell any such securities without registration.

         9.  "MARKET STAND-OFF" AGREEMENT.  Each Holder agrees, if requested by
the Company and an underwriter of Common Stock (or other securities) of the
Company, not to sell or otherwise transfer or dispose of any Class A Common
Stock (or other securities) of the Company held by such Holder during the 180
day period following the effective date of the initial registration statement of
the Company relating to any such securities filed under the Act and during the
90 day period following any subsequent registration statement filed under the
Act.

         If requested by the underwriters, the Holders shall execute a separate
agreement to the foregoing effect.  The Company may impose stop-transfer
instructions with respect to the shares (or securities) subject to the foregoing
restriction until the end of such period.

         10.  TERMINATION.  The registration rights set forth in this Agreement
shall not be available to any Holder if, in the opinion of counsel to the
Company, all of the Registrable Securities then owned by such Holder could be
sold in any 90-day period pursuant to Rule 144 under the Act (without giving
effect to the provisions of Rule 144(k)).  In addition, the registration rights
set forth in this Agreement shall terminate upon the transfer or assignment of
the Registrable Securities or the Class B Stock that is convertible to the Class
A Stock.

         11.  NOTICES.  All communications provided for hereunder shall be sent
by first-class mail or facsimile and (a) if addressed to a Holder, addressed to
the Holder at the address or fax number contained on Schedule A to this
Agreement, or at such other address or fax number as such party shall have
furnished to the Company in writing or (b) if addressed to the Company, at 155
108th Avenue NE, 8th Floor, Bellevue, Washington 98004, Attention:  General
Counsel, or fax number (206) 519-8910 or at such other address or fax number, or
to the attention of such other officer, as the Company shall have furnished to
each Holder of Registrable Securities at the time outstanding.  Notices sent by
first-class mail shall be deemed received three days after the date of deposit
of such notice in the United States mail.  Notices sent by facsimile shall be
deemed received upon receipt by the notified party's facsimile machine.

         12.  NO ASSIGNMENT.  This Agreement is personal to the Holders and
shall not be assignable, by operation of law or otherwise.

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<PAGE>

         13.  DESCRIPTIVE HEADINGS.  The descriptive headings of the several
sections and paragraphs of this Agreement are inserted for reference only and
shall not limit or otherwise affect the meaning hereof.

         14.  GOVERNING LAW.  This Agreement shall be construed and enforced in
accordance with, and the rights of the parties shall be governed by, the laws of
the State of Washington.

         15.  COUNTERPARTS.  This Agreement may be executed simultaneously in
any number of counterparts, each of which shall be deemed an original, but all
such counterparts shall together constitute one and the same instrument.

         IN WITNESS WHEREOF, the parties have caused this agreement to be
executed and delivered by their respective officers thereunto duly authorized as
of the date first above written.

                             EAGLE RIVER INVESTMENTS, L.L.C.


                             By:   /s/ C. James Judson
                                  ----------------------------------
                                  Name:    C. James Judson
                                         ---------------------------
                                  Title:   Manager
                                         ---------------------------

                             NEXTLINK, INC.


                             By:    /s/ R. Bruce Easter, Jr.
                                  ----------------------------------
                                  Name:  R. Bruce Easter, Jr.
                                        ----------------------------
                                  Title:  Vice President
                                        ----------------------------

                             BWP, INC.


                             By:   /s/ Doug Bean
                                  ----------------------------------
                                  Name:   Doug Bean
                                        ----------------------------
                                  Title:  President
                                        ----------------------------

                             ROWENA FAMILY LIMITED LIABILITY COMPANY


                             By:    /s/ Scot B. Jarvis
                                  ----------------------------------
                                  Name:   Scot B. Jarvis
                                        ----------------------------
                                  Title:  Member
                                        ----------------------------

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<PAGE>

                             PENNS LIGHT COMMUNICATIONS, INC.


                             By:    /s/ Gary A. Rawding
                                  ----------------------------------
                                  Name:  Gary A. Rawding
                                        ----------------------------
                                  Title:   President & CEO
                                        ----------------------------

                             PROBE VENTURES CORP.


                             By:      /s/ Victor Schnee
                                  ----------------------------------
                                  Name:    Victor Schnee
                                        ----------------------------
                                  Title:   President
                                        ----------------------------

                             CITY SIGNAL, INC.


                             By:     /s/ R. Postma
                                  ----------------------------------
                                  Name:   R. Postma
                                        ----------------------------
                                  Title:  Secretary & General Counsel
                                        -----------------------------

                             U.S. NETWORK CORPORATION


                             By:                                               
                                  ----------------------------------
                                  Name:                                        
                                        ----------------------------
                                  Title:                                       
                                        ----------------------------
                             


                                                                               
                             ---------------------------------------
                             G. ANDREW BARFUSS



                                                                               
                             ---------------------------------------
                             J. MERRILL BEAN


                                                                               
                             ---------------------------------------
                             JOAN BEAN

                                          13


<PAGE>

                             NEXTLINK COMMUNICATIONS, INC.


                             By:    /s/ R. Bruce Easter, Jr.
                                  ----------------------------------
                                  Name:   R. Bruce Easter, Jr.
                                        ----------------------------
                                  Title:   Vice President
                                        ----------------------------



                                 /s/ Scot B. Jarvis
                             ---------------------------------------
                             SCOT JARVIS

                                          14


<PAGE>

                                      SCHEDULE A

                            HOLDERS' ADDRESSES FOR NOTICES


EAGLE RIVER INVESTMENTS, L.L.C.
c/o C. James Judson
2300 Carillon Point
Kirkland, WA 98033
Fax:  (206)828-8060

NEXTLINK, INC.
c/o R. Bruce Easter, Jr.
155 108th Avenue N.E., Suite 810
Bellevue, WA 98004
Fax:  (206)519-8910

BWP, INC.
c/o Robert Kingery
700 S.W. Washington, 8th Floor
Portland, OR 97205
Fax:  (503)727-6821

ROWENA FAMILY LIMITED LIABILITY COMPANY
c/o Scot Jarvis
4153 Issaquah Pine Lake Road
Issaquah, WA 98029
Fax:  (206)392-9944

PENNS LIGHT COMMUNICATIONS, INC.
c/o Gary Rawding
925 Berkshire Blvd.
Wyomissing, PA 91610
Fax:  (610)288-5666

PROBE VENTURES CORP.
c/o Victor Schnee
Three Wing Drive, Suite 240
Cedar Knolls, NJ 07927-1000
Fax:  (201)285-1519

                                          15


<PAGE>

CITY SIGNAL, INC.
c/o Richard Postma
Miller, Johnson, Snell & Cummiskey
800 Calder Plaza Building
Grand Rapids, MI 49503
Fax:  (616)459-6708

U.S. NETWORK CORPORATION
c/o Ron Gavillet
10 South Riverside Plaza, Suite 401
Chicago, IL 60606-3709
Fax:  (312)906-3636

G. ANDREW BARFUSS
1499 North Cherry Blossom Drive
Farmington, UT 84025-3900
Fax:  (801)451-9708

J. MERRILL BEAN
1972 North 2600 East
Layton, UT 84040
Fax:  (801)451-9708

JOAN BEAN
1972 North 2600 East
Layton, UT 84040
Fax:  (801)451-9708

SCOT JARVIS
4153 Issaquah Pine Lake Road
Issaquah, Washington 98029
Fax:  (206) 392-9944

                                          16