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                                                                     EXHIBIT 4.2



                             XO COMMUNICATIONS, INC.
                 5 3/4% Convertible Subordinated Notes due 2009

                          REGISTRATION RIGHTS AGREEMENT

                                                                     Dated as of
                                                                January 12, 2001

Salomon Smith Barney Inc.
Goldman, Sachs & Co.,
      c/o Salomon Smith Barney Inc.
            388 Greenwich Street,
                  New York, New York 10013

Ladies and Gentlemen:

                XO Communications, Inc., a corporation organized under the laws
of the State of Delaware (the "Company"), proposes to issue and sell to the
Initial Purchasers (as defined herein) upon the terms set forth in the Purchase
Agreement (as defined herein) its 5 3/4% Convertible Subordinated Notes due
2009, convertible into Class A Common Stock, par value $.02 per share, of the
Company (the "Class A Common Stock"). As an inducement to the Initial Purchasers
to enter into the Purchase Agreement and in satisfaction of a condition to the
obligations of the Initial Purchasers thereunder, the Company agrees with the
Initial Purchasers for the benefit of holders (as defined herein) from time to
time of the Registrable Securities (as defined herein) as follows:

        1.      DEFINITIONS. (a) Capitalized terms used herein without
definition shall have the meanings ascribed thereto in the Purchase Agreement.
As used in this Agreement, the following defined terms shall have the following
meanings:

                "Act" or "Securities Act" means the United States Securities Act
of 1933, as amended.

                "Additional Interest" has the meaning assigned thereto in
Section 2(b)(iii) hereof.

                "Affiliate" of any specified person means any other person
which, directly or indirectly, is in control of, is controlled by, or is under
common control with such specified person. For purposes of this definition,
control of a person means the power, direct or indirect, to direct or cause the
direction of the management and policies of such person whether by contract or
otherwise; and the terms "controlling" and "controlled" have meanings
correlative to the foregoing.

                "Commission" means the United States Securities and Exchange
Commission.

                "Effectiveness Period" has the meaning assigned thereto in
Section 2(b)(i) hereof.


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                "Effective Time" means the date on which the Commission declares
the Shelf Registration Statement effective or on which the Shelf Registration
Statement otherwise becomes effective.

                "Electing Holder" has the meaning assigned thereto in Section
3(a)(3) hereof.

                "Exchange Act" means the United States Securities Exchange Act
of 1934, as amended.

                The term "holder" means, when used with respect to any Security,
the Holder (as defined in the Indenture) and, with respect to any Class A Common
Stock, the record holder of such Class A Common Stock.

                "Indenture" shall mean the Indenture, dated as of January 12,
2001, between the Company and U.S. Trust Company, National Association, as
Trustee.

                "Initial Purchasers" means you.

                "Managing Underwriters" means the investment banker or
investment bankers and manager or managers that shall administer an underwritten
offering, if any, conducted pursuant to Section 6 hereof.

                "NASD Rules" means the Rules of the National Association of
Securities Dealers, Inc., as amended from time to time.

                "Notice and Questionnaire" means a Notice of Registration
Statement and Selling Securityholder Questionnaire substantially in the form of
Exhibit A hereto.

                "Person" means an individual, partnership, corporation, trust or
unincorporated organization, or a government or agency or political subdivision
thereof.

                "Prospectus" means the prospectus (including, without
limitation, any preliminary prospectus, any final prospectus and any prospectus
that discloses information previously omitted from a prospectus filed as part of
an effective registration statement in reliance upon Rule 430A under the Act)
included in the Shelf Registration Statement, as amended or supplemented by any
prospectus supplement with respect to the terms of the offering of any portion
of the Registrable Securities covered by the Shelf Registration Statement and by
all other amendments and supplements to such prospectus, including all material
incorporated by reference in such prospectus and all documents filed after the
date of such prospectus by the Company under the Exchange Act and incorporated
by reference therein.

                "Purchase Agreement" means the purchase agreement dated January
5, 2001, between the Initial Purchasers and the Company.

                "Registrable Securities" means all or any portion of the
Securities and the shares of Class A Common Stock issuable upon conversion of
such Securities and any Class A Common Stock or securities of the Company issued
in exchange for or in respect of such Class A Common Stock or securities,
whether as the result of any stock split or reclassification of, or



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stock dividend on, such Class A Common Stock or otherwise; provided, however,
that a security ceases to be a Registrable Security when it is no longer a
Restricted Security.

                "Registration Default" has the meaning assigned thereto in
Section 2(b)(iii) hereof.

                "Restricted Security" means any Security or share of Class A
Common Stock issued or issuable upon conversion of any Security, except any
Security or share of Class A Common Stock which (i) has been effectively
registered under the Securities Act and sold in a manner contemplated by the
Shelf Registration Statement, or (ii) has been transferred in compliance with
Rule 144 under the Securities Act (or any successor provision thereto) or is
transferable pursuant to paragraph (k) of such Rule 144 (or any successor
provision thereto), (iii) has been sold in compliance with Regulation S under
the Securities Act (or any successor thereto) and does not constitute the unsold
allotment of a distributor within the meaning of Regulation S under the
Securities Act or (iv) has otherwise been transferred and a new Security or
share of Class A Common Stock not subject to transfer restrictions under the
Securities Act has been delivered by or on behalf of the Company.

                "Rules and Regulations" means the published rules and
regulations of the Commission promulgated under the Securities Act or the
Exchange Act, as in effect at any relevant time.

                "Shelf Registration" means a registration effected pursuant to
Section 2 hereof.

                "Shelf Registration Statement" means a "shelf" registration
statement filed under the Securities Act providing for the registration of, and
the sale on a continuous or delayed basis by the holders of, all of the
Registrable Securities pursuant to Rule 415 under the Securities Act and/or any
similar rule that may be adopted by the Commission, filed by the Company
pursuant to the provisions of Section 2 of this Agreement, including the
Prospectus contained therein, any amendments and supplements to such
registration statement, including post-effective amendments, and all exhibits
and all material incorporated by reference in such registration statement.

                "Suspension Period" shall have the meaning assigned thereto in
Section 3(j) hereof.

                The term "underwriter" means any underwriter of Registrable
Securities in connection with an offering thereof under a Shelf Registration
Statement.

                (b)     Wherever there is a reference in this Agreement to a
        percentage of Registrable Securities, Class A Common Stock shall be
        treated as representing the aggregate principal amount of Securities
        which was surrendered for conversion or exchange in order to receive
        such number of shares of Class A Common Stock.

        2.      SHELF REGISTRATION. (a) The Company shall file with the
Commission a Shelf Registration Statement relating to the offer and sale of the
Registrable Securities and shall use its best efforts to cause such Shelf
Registration Statement to be declared effective under the Act on or prior to 180
days after the Closing Date (as defined in the Purchase Agreement), provided,



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however, that no holder shall be entitled to be named as a selling
securityholder in the Shelf Registration Statement or to use the Prospectus
forming a part thereof for resales of Registrable Securities unless such holder
is an Electing Holder.

                (b)     The Company shall use its reasonable best efforts:

                        (i)     To keep the Shelf Registration Statement
                                continuously effective in order to permit the
                                Prospectus forming part thereof to be usable by
                                holders for resales of Registrable Securities
                                for a period ending two years from the last
                                Closing Time (as defined in the Purchase
                                Agreement), or such shorter period that will
                                terminate when there are no Registrable
                                Securities outstanding (in either case, such
                                period being referred to herein as the
                                "Effectiveness Period");

                        (ii)    After the Effective Time of the Shelf
                                Registration Statement, promptly upon the
                                request of any holder of Registrable Securities
                                that is not then an Electing Holder, to take any
                                action reasonably necessary to enable such
                                holder to use the Prospectus forming a part
                                thereof for resales of Registrable Securities,
                                including, without limitation, any action
                                necessary to identify such holder as a selling
                                securityholder in the Shelf Registration
                                Statement; provided, however, that nothing in
                                this subparagraph shall relieve such holder of
                                the obligation to return a completed and signed
                                Notice and Questionnaire to the Company in
                                accordance with Section 3(a)(2) hereof; and

                        (iii)   If the Shelf Registration Statement is not
                                declared effective by the Commission on or prior
                                to the date specified for such effectiveness in
                                (a) above or (B) the Shelf Registration
                                Statement is declared effective but thereafter
                                ceases to be effective or usable in connection
                                with resales of Restricted Securities during the
                                Effectiveness Period (each such event referred
                                to in clause (A) or (B) above a "Registration
                                Default"), then additional interest will accrue
                                (in addition to the stated interest on the
                                Securities) at the rate of 0.25% per annum on
                                the principal amount of the Securities,
                                determined daily (calculated on the same basis
                                as interest on the Securities shall be
                                calculated) for the period from the occurrence
                                of the Registration Default until such time as
                                no Registration Default is in effect (after
                                which time no special interest will accrue).
                                Such additional interest (the "Additional
                                Interest") will be payable in cash semi-annually
                                in arrears on each January and July in
                                accordance with the Indenture. For each 90-day
                                period that the Registration Default continues,
                                the per annum rate of such Additional Interest
                                will increase by an additional 0.25%; provided
                                that such rate shall in no event exceed 0.5% per
                                annum in the aggregate. At such time as such
                                Registration Default is no longer



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                                in effect, the interest rate on the Securities
                                shall be 5 3/4% and no further Additional
                                Interest will accrue.

The Company shall be deemed not to have used its best efforts (within the
meaning of Section 4(i) of the Purchase Agreement) to keep the Shelf
Registration Statement effective during the Effectiveness Period if the Company
voluntarily takes any action that would result in Electing Holders not being
able to offer and sell any of their Registrable Securities during such period,
unless (i) such action is required by applicable law, or (ii) the Company
determines based upon the advice of counsel that is advisable to disclose in the
Shelf Registration Statement a financing, acquisition or other corporate
transaction, and the Board of Directors of the Company shall have determined in
good faith that such disclosure is not in the best interests of the Company and
its stockholders, and, in the case of clause (i) above, the Company thereafter
promptly complies with the requirements of paragraph 3(j) below. Notwithstanding
Section 2(b)(iii) above, additional interest shall not accrue under the
circumstances contemplated by clauses (i) and (ii) above, so long as the
effectiveness of the Shelf Registration Statement is not suspended for more than
30 days in any three month period or for three periods not to exceed an
aggregate of 90 days in any twelve-month period during the Effectiveness Period.

                (c)     Any shares of Class A Common Stock issued or issuable
        upon the exercise of a holder's right pursuant to Section 1201 of the
        Indenture to require the Company to repurchase any or all of a holder's
        Securities upon the occurrence of a Change of Control (as defined in the
        Indenture) shall be deemed "Registrable Securities" for the purposes of
        this Agreement for so long as such securities constitute Restricted
        Securities. The Company shall include such securities in the Shelf
        Registration Statement filed pursuant to (a) above, or file a new Shelf
        Registration Statement relating to the offer and sale of such securities
        and shall use its best efforts to cause such Shelf Registration
        Statement to be declared effective under the Act on or prior to 60 days
        from the expiration date of the Designated Event Offer pursuant to which
        such securities were issued in compliance with the procedures set forth
        in (b) above (except that any reference to the date of effectiveness in
        (b) shall be as specified in this clause (c)).

        3.      REGISTRATION PROCEDURES. In connection with the Shelf
Registration Statement, the following provisions shall apply:

                (a)     (i) Not less than 30 calendar days prior to the
        Effective Time of the Shelf Registration Statement, the Company shall
        mail the Notice and Questionnaire to the holders of Registrable
        Securities. No holder shall be entitled to be named as a selling
        security holder in the Shelf Registration Statement as of the Effective
        Time, and no holder shall be entitled to use the Prospectus forming a
        part thereof for resales of Registrable Securities at any time, unless
        such holder has returned a completed and signed Notice and Questionnaire
        to the Company by the deadline for response set forth therein; provided,
        however, holders of Registrable Securities shall have at least 15
        calendar days from the date on which the Notice and Questionnaire is
        first mailed to such holders to return a completed and signed Notice and
        Questionnaire to the Company.

                        (ii)    After the Effective Time of the Shelf
                                Registration Statement, the Company shall, upon
                                the request of any holder of Registrable



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                                Securities that has not previously received a
                                Notice and Questionnaire, promptly send a Notice
                                and Questionnaire to such holder, and such
                                holder must return a completed and signed Notice
                                and Questionnaire to the Company by the deadline
                                for response set forth therein (not to be less
                                than 15 calendar days from the date on which the
                                Notice and Questionnaire is first mailed to such
                                holders). The Company shall not be required to
                                take any action to name such holder as a selling
                                securityholder in the Shelf Registration
                                Statement or to enable such holder to use the
                                Prospectus forming a part thereof for resales of
                                Registrable Securities until such holder has
                                returned a completed and signed Notice and
                                Questionnaire to the Company.

                        (iii)   The term "Electing Holder" shall mean any holder
                                of Registrable Securities that has returned a
                                completed and signed Notice and Questionnaire to
                                the Company within the required time period in
                                accordance with Section 3(a)(1) or 3(a)(2)
                                hereof.

                (b)     The Company shall furnish to each Electing Holder, prior
        to the Effective Time, a copy of the Shelf Registration Statement
        initially filed with the Commission, and shall furnish to such holders,
        prior to the filing thereof with the Commission, copies of each
        amendment thereto and each amendment or supplement, if any, to the
        Prospectus included therein, and shall use its best efforts to reflect
        in each such document, at the Effective Time or when so filed with the
        Commission, as the case may be, such comments as such holders and their
        respective counsel reasonably may propose.

                (c)     The Company shall promptly take such action as may be
        necessary so that (i) each of the Shelf Registration Statement and any
        amendment thereto and the Prospectus forming part thereof and any
        amendment or supplement thereto (and each report or other document
        incorporated therein by reference in each case) complies in all material
        respects with the Securities Act and the Exchange Act and the respective
        rules and regulations thereunder, (ii) each of the Shelf Registration
        Statement and any amendment thereto does not, when it becomes effective,
        contain an untrue statement of a material fact or omit to state a
        material fact required to be stated therein or necessary to make the
        statements therein not misleading and (iii) each of the Prospectus
        forming part of the Shelf Registration Statement, and any amendment or
        supplement to such Prospectus, does not at any time during the
        Effectiveness Period include an untrue statement of a material fact or
        omit to state a material fact necessary in order to make the statements
        therein, in the light of the circumstances under which they were made,
        not misleading.

                (d)     The Company shall promptly advise each Electing Holder,
        and shall confirm such advice in writing if so requested by any such
        holder:

                        (i)     when the Shelf Registration Statement and any
                                amendment thereto has been filed with the
                                Commission and when the Shelf



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                                Registration Statement or any post-effective
                                amendment thereto has become effective;

                        (ii)    of any request by the Commission for amendments
                                or supplements to the Shelf Registration
                                Statement or the Prospectus included therein or
                                for additional information;

                        (iii)   of the issuance by the Commission of any stop
                                order suspending the effectiveness of the Shelf
                                Registration Statement or the initiation of any
                                proceedings for such purpose;

                        (iv)    of the receipt by the Company of any
                                notification with respect to the suspension of
                                the qualification of the securities included in
                                the Shelf Registration Statement for sale in any
                                jurisdiction or the initiation of any proceeding
                                for such purpose; and

                        (v)     of the happening of any event or the existence
                                of any state of facts that requires the making
                                of any changes in the Shelf Registration
                                Statement or the Prospectus included therein so
                                that, as of such date, such Shelf Registration
                                Statement and Prospectus do not contain an
                                untrue statement of a material fact and do not
                                omit to state a material fact required to be
                                stated therein or necessary to make the
                                statements therein (in the case of the
                                Prospectus, in light of the circumstances under
                                which they were made) not misleading (which
                                advice shall be accompanied by an instruction to
                                such holders to suspend the use of the
                                Prospectus until the requisite changes have been
                                made).

                (e)     The Company shall use its best efforts to prevent the
        issuance, and if issued to obtain the withdrawal, of any order
        suspending the effectiveness of the Shelf Registration Statement at the
        earliest possible time.

                (f)     The Company shall furnish to each Electing Holder,
        without charge, at least one copy of the Shelf Registration Statement
        and all post-effective amendments thereto, including financial
        statements and schedules.

                (g)     The Company shall, during the Effectiveness Period,
        deliver to each Electing Holder, without charge, as many copies of the
        Prospectus (including each preliminary Prospectus) included in the Shelf
        Registration Statement and any amendment or supplement thereto as such
        Electing Holder may reasonably request; and the Company consents (except
        during the continuance of any event described in Section 3(d)(5) above)
        to the use of the Prospectus and any amendment or supplement thereto by
        each of the Electing Holders in connection with the offering and sale of
        the Registrable Securities covered by the Prospectus and any amendment
        or supplement thereto during the Effectiveness Period.

                (h)     Prior to any offering of Registrable Securities pursuant
        to the Shelf Registration Statement, the Company shall (1) register or
        qualify or cooperate with the



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        Electing Holders and their respective counsel in connection with the
        registration or qualification of such Registrable Securities for offer
        and sale under the securities or "blue sky" laws of such jurisdictions
        within the United States as any Electing Holder may reasonably request,
        (2) keep such registrations or qualifications in effect and comply with
        such laws so as to permit the continuance of offers and sales in such
        jurisdictions for so long as may be necessary to enable any Electing
        Holder or underwriter, if any, to complete its distribution of
        Registrable Securities pursuant to the Shelf Registration Statement, and
        (3) take any and all other actions necessary or advisable to enable the
        disposition in such jurisdictions of such Registrable Securities;
        provided, however, that in no event shall the Company be obligated to
        (i) qualify as a foreign corporation or as a dealer in securities in any
        jurisdiction where it would not otherwise be required to so qualify but
        for this Section 3(h) or (ii) file any general consent to service of
        process in any jurisdiction where it is not as of the date hereof so
        subject.

                (i)     Unless any Registrable Securities shall be in book-entry
        only form, the Company shall cooperate with the Electing Holders to
        facilitate the timely preparation and delivery of certificates
        representing Registrable Securities to be sold pursuant to the Shelf
        Registration Statement, which certificates, if so required by any
        securities exchange upon which any Registrable Securities are listed,
        shall be penned, lithographed or engraved, or produced by any
        combination of such methods, on steel engraved borders, and which
        certificates shall be free of any restrictive legends and in such
        permitted denominations and registered in such names as Electing Holders
        may request in connection with the sale of Registrable Securities
        pursuant to the Shelf Registration Statement.

                (j)     Upon the occurrence of any fact or event contemplated by
        paragraph 3(d)(5) above, the Company shall promptly prepare a
        post-effective amendment or supplement to the Shelf Registration
        Statement or the Prospectus, or any document incorporated therein by
        reference, or file any other required document so that, as thereafter
        delivered to purchasers of the Registrable Securities included therein,
        the Prospectus will not include an untrue statement of a material fact
        or omit to state any material fact necessary to make the statements
        therein, in the light of the circumstances under which they were made,
        not misleading; provided, however, if the Company determines based upon
        the advice of counsel that it is advisable to disclose in the Shelf
        Registration Statement a financing, acquisition or other corporate
        transaction, and the Board of Directors of the Company shall have
        determined in good faith that such disclosure would not be in the best
        interests of the Company and its stockholders, the Company shall not be
        required to prepare and file such amendment, supplement or document for
        such period (a "Suspension Period") as the Board of Directors of the
        Company shall have determined in good faith is in the best interests of
        the Company. If the Company notifies the Electing Holders of the
        occurrence of any event contemplated by paragraph 3(d)(5) above, each
        Electing Holder agrees, as a consequence of the inclusion of any of such
        holder's Registrable Securities in the Shelf Registration Statement, to
        suspend the use of the Prospectus until the requisite changes to the
        Prospectus have been made.



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                (k)     Not later than the Effective Time of the Shelf
        Registration Statement, the Company shall provide CUSIP numbers for the
        Registrable Securities.

                (l)     The Company shall use its best efforts to comply with
        all applicable Rules and Regulations, and to make generally available to
        its securityholders as soon as practicable, but in any event not later
        than eighteen months after (i) the effective date (as defined in Rule
        158(c) under the Securities Act) of the Shelf Registration Statement,
        (ii) the effective date of each post-effective amendment to the Shelf
        Registration Statement, and (iii) the date of each filing by the Company
        with the Commission of an Annual Report on Form 10-K that is
        incorporated by reference in the Shelf Registration Statement, an
        earning statement of the Company and its subsidiaries complying with
        Section 11(a) of the Securities Act and the rules and regulations of the
        Commission thereunder (including, at the option of the Company, Rule
        158).

                (m)     In the event of an underwritten offering conducted
        pursuant to Section 6 hereof, the Company shall, if requested, promptly
        include or incorporate in a prospectus supplement or post-effective
        amendment to the Shelf Registration Statement such information as the
        Managing Underwriters reasonably agree should be included therein and to
        which the Company does not reasonably object and shall make all required
        filings of such prospectus supplement or post-effective amendment as
        soon as practicable after it is notified of the matters to be included
        or incorporated in such prospectus supplement or post-effective
        amendment.

                (n)     The Company shall enter into such customary agreements
        (including an underwriting agreement in customary form in the event of
        an underwritten offering conducted pursuant to Section 6 hereof) and
        take all other appropriate action in order to expedite and facilitate
        the registration and disposition of the Registrable Securities, and in
        connection therewith, if an underwriting agreement is entered into,
        cause the same to contain indemnification provisions and procedures
        substantially identical to those set forth in Section 5 hereof with
        respect to all parties to be indemnified pursuant to Section 5 hereof.

                (o)     The Company shall:

                        (i)     (A) make reasonably available for inspection by
                                Electing Holders, any underwriter participating
                                in any disposition pursuant to the Shelf
                                Registration Statement, and any attorney,
                                accountant or other agent retained by such
                                holders or any such underwriter all relevant
                                financial and other records, pertinent corporate
                                documents and properties of the Company and its
                                subsidiaries, and (B) cause the Company's
                                officers, directors and employees to supply all
                                information reasonably requested by such holders
                                or any such underwriter, attorney, accountant or
                                agent in connection with the Shelf Registration
                                Statement, in each case, as is customary for
                                similar due diligence examinations; provided,
                                however, that all records, information and
                                documents that are designated in writing by the
                                Company, in good faith, as confidential shall be
                                kept



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                                confidential by such holders and any such
                                underwriter, attorney, accountant or agent,
                                unless such disclosure is made in connection
                                with a court proceeding or required by law, or
                                such records, information or documents become
                                available to the public generally or through a
                                third party without an accompanying obligation
                                of confidentiality; and provided further that,
                                if the foregoing inspection and information
                                gathering would otherwise disrupt the Company's
                                conduct of its business, such inspection and
                                information gathering shall, to the greatest
                                extent possible, be coordinated on behalf of the
                                Electing Holders and the other parties entitled
                                thereto by one counsel designated by and on
                                behalf of Electing Holders and other parties;

                        (ii)    in connection with any underwritten offering
                                conducted pursuant to Section 6 hereof, make
                                such representations and warranties to the
                                holders participating in such underwritten
                                offering and to the Managing Underwriters, in
                                form, substance and scope as are customarily
                                made by the Company to underwriters in primary
                                underwritten offerings of equity and convertible
                                debt securities and covering matters including,
                                but not limited to, those set forth in the
                                Purchase Agreement;

                        (iii)   in connection with any underwritten offering
                                conducted pursuant to Section 6 hereof, obtain
                                opinions of counsel to the Company (which
                                counsel and opinions (in form, scope and
                                substance) shall be reasonably satisfactory to
                                the Managing Underwriters) addressed to each
                                holder participating in such underwritten
                                offering and the underwriters, covering such
                                matters as are customarily covered in opinions
                                requested in primary underwritten offerings of
                                equity and convertible debt securities and such
                                other matters as may be reasonably requested by
                                such holders and underwriters (it being agreed
                                that the matters to be covered by such opinions
                                shall include, without limitation, as of the
                                date of the opinion and as of the Effective Time
                                of the Shelf Registration Statement or most
                                recent post-effective amendment thereto, as the
                                case may be, the absence from the Shelf
                                Registration Statement and the Prospectus,
                                including the documents incorporated by
                                reference therein; of an untrue statement of a
                                material fact or the omission of a material fact
                                required to be stated therein or necessary to
                                make the statements therein not misleading);

                        (iv)    in connection with any underwritten offering
                                conducted pursuant to Section 6 hereof, obtain
                                "cold comfort" letters and updates thereof from
                                the independent public accountants of the
                                Company (and, if necessary, from the independent
                                public accountants of any subsidiary of the
                                Company or of any business acquired by the
                                Company for which financial statements and
                                financial data are, or



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                                are required to be, included in the Shelf
                                Registration Statement), addressed to each
                                holder participating in such underwritten
                                offering (if such holder has provided such
                                letter, representations or documentation, if
                                any, required for such cold comfort letter to be
                                so addressed) underwriters, in customary form
                                and covering matters of the type customarily
                                covered in "cold comfort" letters in connection
                                with primary underwritten offerings;

                        (v)     in connection with any underwritten offering
                                conducted pursuant to Section 6 hereof, deliver
                                such documents and certificates as may be
                                reasonably requested by any holders
                                participating in such underwritten offering and
                                the Managing Underwriters, if any, including,
                                without limitation, certificates to evidence
                                compliance with Section 3(j) hereof and with any
                                conditions contained in the underwriting
                                agreement or other agreements entered into by
                                the Company.

                (p)     The Company will use its best efforts to cause the Class
        A Common Stock issuable upon conversion of the Securities to be listed
        for quotation on the Nasdaq National Market or other stock exchange or
        trading system on which the Class A Common Stock primarily trades on or
        prior to the Effective Time of the Shelf Registration Statement
        hereunder.

                (q)     In the event that any broker-dealer registered under the
        Exchange Act shall be an "affiliate" (as defined in Rule 2720(b)(1) of
        the NASD Rules (or any successor provision thereto)) of the Company or
        has a "conflict of interest" (as defined in Rule 2720(b)(7) of the NASD
        Rules (or any successor provision thereto)) and such broker-dealer shall
        underwrite, participate as a member of an underwriting syndicate or
        selling group or assist in the distribution of any Registrable
        Securities covered by the Shelf Registration Statement, whether as a
        holder of such Registrable Securities or as an underwriter, a placement
        or sales agent or a broker or dealer in respect thereof, or otherwise,
        the Company shall assist such broker-dealer in complying with the
        requirements of the NASD Rules, including, without limitation, by (A)
        engaging a "qualified independent underwriter" (as defined in Rule
        2720(b)(15) of the NASD Rules (or any successor provision thereto)) to
        participate in the preparation of the registration statement relating to
        such Registrable Securities, to exercise usual standards of due
        diligence in respect thereto and to recommend the public offering price
        of such Registrable Securities, (B) indemnifying such qualified
        independent underwriter to the extent of the indemnification of
        underwriters provided in Section 5 hereof, and (C) providing such
        information to such broker-dealer as may be required in order for such
        broker-dealer to comply with the requirements of the NASD Rules.

                (r)     The Company shall use its best efforts to take all other
        steps necessary to effect the registration, offering and sale of the
        Registrable Securities covered by the Shelf Registration Statement
        contemplated hereby.



                                       11
<PAGE>   12

        4.      REGISTRATION EXPENSES. The Company shall bear all fees and
expenses incurred in connection with the performance of its obligations under
Sections 2, 3 and 6 hereof and the fees reasonable and expenses of a single
counsel to the Initial Purchasers. In addition, in the event of an underwritten
offering of Registrable Securities conducted pursuant to Section 6 hereof, or if
in any other event the Company requires that inspection and information
gathering be coordinated by reasonable counsel for the Electing Holders as
provided in Section 3(o)(i) hereof, the Company shall pay the reasonable fees
and expenses of a single counsel selected by the Electing Holders of not less
than 25% of the Registrable Securities to be included in such underwritten
offering (or, in any such other event, included in the Shelf Registration
Statement) to represent them. The Electing Holders participating in such
offering (or, in any such other event, participating in such inspection and
information gathering) shall be responsible, on a pro rata basis based on the
respective amount of their Registrable Securities included in such offering, for
all fees and expenses of such counsel in excess of $25,000.

        5.      INDEMNIFICATION AND CONTRIBUTION.

                (a)     Indemnification by the Company. Upon the registration of
        the Registrable Securities pursuant to Section 2 hereof, the Company
        shall indemnify and hold harmless each Electing Holder and each
        underwriter, selling agent or other securities professional, if any,
        which facilitates the disposition of Registrable Securities, and each of
        their respective officers and directors and each person who controls
        such Electing Holder, underwriter, selling agent or other securities
        professional within the meaning of Section 15 of the Securities Act or
        Section 20 of the Exchange Act (each such person being sometimes
        referred to as an "Indemnified Person") against any losses, claims,
        damages or liabilities, joint or several, to which such Indemnified
        Person may become subject under the Securities Act or otherwise, insofar
        as such losses, claims, damages or liabilities (or actions in respect
        thereof) arise out of or are based upon an untrue statement or alleged
        untrue statement of a material fact contained in any Shelf Registration
        Statement under which such Registrable Securities are to be registered
        under the Securities Act, or any Prospectus contained therein or
        furnished by the Company to any Indemnified Person, or any amendment or
        supplement thereto, or arise out of or are based upon the omission or
        alleged omission to state therein a material fact required to be stated
        therein or necessary to make the statements therein not misleading, and
        the Company hereby agrees to reimburse such Indemnified Person for any
        legal or other expenses reasonably incurred by them in connection with
        investigating or defending any such action or claim as such expenses are
        incurred; provided, however, that the Company shall not be liable to any
        such Indemnified Person in any such case to the extent that any such
        loss, claim, damage or liability arises out of or is based upon an
        untrue statement or alleged untrue statement or omission or alleged
        omission made in such Shelf Registration Statement or Prospectus, or
        amendment or supplement, in reliance upon and in conformity with written
        information furnished to the Company by such Indemnified Person
        expressly for use therein.

                (b)     Indemnification by the Holders and any Agents and
        Underwriters. Each Electing Holder agrees, as a consequence of the
        inclusion of any of such holder's Registrable Securities in such Shelf
        Registration Statement, and each underwriter, selling agent or other
        securities professional, if any, which facilitates the disposition of



                                       12
<PAGE>   13

        Registrable Securities shall agree, as a consequence of facilitating
        such disposition of Registrable Securities, severally and not jointly,
        to (i) indemnify and hold harmless the Company, its directors, officers
        who sign any Shelf Registration Statement and each person, if any, who
        controls the Company within the meaning of either Section 15 of the
        Securities Act or Section 20 of the Exchange Act, against any losses,
        claims, damages or liabilities to which the Company or such other
        persons may become subject, under the Securities Act or otherwise,
        insofar as such losses, claims, damages or liabilities (or actions in
        respect thereof) arise out of or are based upon an untrue statement or
        alleged untrue statement of a material fact contained in such Shelf
        Registration Statement or Prospectus, or any amendment or supplement, or
        arise out of or are based upon the omission or alleged omission to state
        therein a material fact required to be stated therein or necessary to
        make the statements therein not misleading, in each case to the extent,
        but only to the extent, that such untrue statement or alleged untrue
        statement or omission or alleged omission was made in reliance upon and
        in conformity with written information furnished to the Company by such
        holder, underwriter, selling agent or other securities professional
        expressly for use therein, and (ii) reimburse the Company for any legal
        or other expenses reasonably incurred by the Company in connection with
        investigating or defending any such action or claim as such expenses are
        incurred.

                (c)     Notices of Claims, Etc. Promptly after receipt by an
        indemnified party under subsection (a) or (b) above of notice of the
        commencement of any action, such indemnified party shall, if a claim in
        respect thereof is to be made against an indemnifying party under this
        Section 5, notify such indemnifying party in writing of the commencement
        thereof; but the omission so to notify the indemnifying party shall not
        relieve it from any liability which it may have to any indemnified party
        otherwise than under this Section 5. In case any such action shall be
        brought against any indemnified party and it shall notify an
        indemnifying party of the commencement thereof, such indemnifying party
        shall be entitled to participate therein and, to the extent that it
        shall wish, jointly with any other indemnifying party similarly
        notified, to assume the defense thereof, with counsel reasonably
        satisfactory to such indemnified party (who shall not, except with the
        consent of the indemnified party, be counsel to the indemnifying party),
        and, after notice from the indemnifying party to such indemnified party
        of its election so to assume the defense thereof, such indemnifying
        party shall not be liable to such indemnified party under this Section 5
        for any legal expenses of other counsel or any other expenses, in each
        case subsequently incurred by such indemnified party, in connection with
        the defense thereof other than reasonable costs of investigation. No
        indemnifying party shall, without the written consent of the indemnified
        party, effect the settlement or compromise of, or consent to the entry
        of any judgment with respect to, any pending or threatened action or
        claim in respect of which indemnification or contribution may be sought
        hereunder (whether or not the indemnified party is an actual or
        potential party to such action or claim) unless such settlement,
        compromise or judgment (i) includes an unconditional release of the
        indemnified party from all liability arising out of such action or claim
        provided, that such unconditional release may be subject to a parallel
        release of a claimant or plaintiff by such indemnified party from all
        liability in respect of claims or counter claims asserted by such
        indemnified party and (ii) does not include a statement as to, or an
        admission of, fault, culpability or a failure to act, by or on behalf of
        any indemnified party.



                                       13
<PAGE>   14

                (d)     Contribution. If the indemnification provided for in
        this Section 5 is unavailable to or insufficient to hold harmless an
        indemnified party under subsection (a) or (b) above in respect of any
        losses, claims, damages or liabilities (or actions in respect thereof)
        referred to therein, then each indemnifying party shall contribute to
        the amount paid or payable by such indemnified party as a result of such
        losses, claims, damages or liabilities (or actions in respect thereof)
        in such proportion as is appropriate to reflect the relative fault of
        the indemnifying party and the indemnified party in connection with the
        statements or omissions which resulted in such losses, claims, damages
        or liabilities (or actions in respect thereof), as well as any other
        relevant equitable considerations. The relative fault of such
        indemnifying party and indemnified party shall be determined by
        reference to, among other things, whether the untrue or alleged untrue
        statement of a material fact or omission or alleged omission to state a
        material fact relates to information supplied by such indemnifying party
        or by such indemnified party, and the parties' relative intent,
        knowledge, access to information and opportunity to correct or prevent
        such statement or omission. The parties hereto agree that it would not
        be just and equitable if contribution pursuant to this Section 5(d) were
        determined by pro rata allocation (even if the Electing Holders or any
        underwriters, selling agents or other securities professionals or all of
        them were treated as one entity for such purpose) or by any other method
        of allocation which does not take account of the equitable
        considerations referred to in this Section 5(d). The amount paid or
        payable by an indemnified party as a result of the losses, claims,
        damages or liabilities (or actions in respect thereof) referred to above
        shall be deemed to include any legal or other fees or expenses
        reasonably incurred by such indemnified party in connection with
        investigating or defending any such action or claim. No person guilty of
        fraudulent misrepresentation (within the meaning of Section 11(f) of the
        Securities Act) shall be entitled to contribution from any person who
        was not guilty of such fraudulent misrepresentation. The obligations of
        the Electing Holders and any underwriters, selling agents or other
        securities professionals in this Section 5(d) to contribute shall be
        several in proportion to the percentage of principal amount of
        Registrable Securities registered or underwritten, as the case may be,
        by them and not joint.

                (e)     Notwithstanding any other provision of this Section 5,
        in no event will any (i) Electing Holder be required to undertake
        liability to any person under this Section 5 for any amounts in excess
        of the dollar amount of the proceeds to be received by such holder from
        the sale of such holder's Registrable Securities (after deducting any
        fees, discounts and commissions applicable thereto) pursuant to any
        Shelf Registration Statement under which such Registrable Securities are
        to be registered under the Securities Act and (ii) underwriter, selling
        agent or other securities professional be required to undertake
        liability to any person hereunder for any amounts in excess of the
        discount, commission or other compensation payable to such underwriter,
        selling agent or other securities professional with respect to the
        Registrable Securities underwritten by it and distributed to the public.

                (f)     The obligations of the Company under this Section 5
        shall be in addition to any liability which the Company may otherwise
        have to any Indemnified Person and the obligations of any Indemnified
        Person under this Section 5 shall be in addition to any liability which
        such Indemnified Person may otherwise have to the Company. The



                                       14
<PAGE>   15

        remedies provided in this Section 5 are not exclusive and shall not
        limit any rights or remedies which may otherwise be available to an
        indemnified party at law or in equity.

        6.      UNDERWRITTEN OFFERING. Any holder of Registrable Securities who
desires to do so may sell Registrable Securities (in whole or in part) in an
underwritten offering; provided that (i) the Electing Holders of at least 331/3%
in aggregate principal amount of the Registrable Securities then covered by the
Shelf Registration Statement shall request such an offering , (ii) the aggregate
principal amount of Registrable Securities included in any underwritten offering
shall not be less than $25 million and (iii) at least such aggregate principal
amount of such Registrable Securities shall be included in such offering; and
provided further that the Company shall not be obligated to cooperate with more
than one underwritten offering during the Effectiveness Period. Upon receipt of
such a request, the Company shall provide all holders of Registrable Securities
written notice of the request, which notice shall inform such holders that they
have the opportunity to participate in the offering. In any such underwritten
offering, the investment banker or bankers and manager or managers that will
administer the offering will be selected by, and the underwriting arrangements
with respect thereto (including the size of the offering) will be approved by,
the holders of a majority of the Registrable Securities to be included in such
offering; provided, however, that such investment bankers and managers and
underwriting arrangements must be reasonably satisfactory to the Company. No
holder may participate in any underwritten offering contemplated hereby unless
(a) such holder agrees to sell such holder's Registrable Securities to be
included in the underwritten offering in accordance with any approved
underwriting arrangements, (b) such holder completes and executes all reasonable
questionnaires, powers of attorney, indemnities, underwriting agreements,
lock-up letters and other documents required under the terms of such approved
underwriting arrangements, and (c) if such holder is not then an Electing
Holder, such holder returns a completed and signed Notice and Questionnaire to
the Company in accordance with Section 3(a)(2) hereof within a reasonable amount
of time before such underwritten offering. The holders participating in any
underwritten offering shall be responsible for any underwriting discounts and
commissions and fees including the fees of any qualified independent underwriter
and, subject to Section 4 hereof, expenses of their own counsel. The Company
shall pay all expenses customarily borne by issuers, including but not limited
to filing fees, the fees and disbursements of its counsel and independent public
accountants and any printing expenses incurred in connection with such
underwritten offering. Notwithstanding the foregoing or the provisions of
Section 3(m) hereof, upon receipt of a request from the Managing Underwriter or
a representative of holders of a majority in principal amount of the Registrable
Securities to be included in an underwritten offering to prepare and file an
amendment or supplement to the Shelf Registration Statement and Prospectus in
connection with an underwritten offering, the Company may delay the filing of
any such amendment or supplement for up to 90 days if the Board of Directors of
the Company shall have determined in good faith that the Company has a bona fide
business reason for such delay.

        7.      MISCELLANEOUS.

                (a)     Other Registration Rights. The Company may grant
        registration rights that would permit any Person that is a third party
        the right to piggy-back on any Shelf Registration Statement, provided
        that if the Managing Underwriter of any underwritten offering conducted
        pursuant to Section 6 hereof notifies the Company and the Electing



                                       15
<PAGE>   16

        Holders that the total amount of securities which the Electing Holders
        and the holders of such piggy-back rights intend to include in any Shelf
        Registration Statement is so large as to materially threaten the success
        of such offering (including the price at which such securities can be
        sold), then the amount, number or kind of securities to be offered for
        the account of holders of such piggy-back rights will be reduced to the
        extent necessary to reduce the total amount of securities to be included
        in such offering to the amount, number and kind recommended by the
        Managing Underwriter prior to any reduction in the amount of Registrable
        Securities to be included in such Shelf Registration Statement; provided
        that, with respect to registration rights granted by the Company prior
        to the date hereof, no cutback pursuant to this Section shall be
        required to the extent such cutback would conflict with such previously
        granted registration rights.

                (b)     Amendments and Waivers. This Agreement, including this
        Section 7(b), may be amended, and waivers or consents to departures from
        the provisions hereof may be given, only by a written instrument duly
        executed by the Company and the holders of a majority in aggregate
        principal amount of Registrable Securities then outstanding. Each holder
        of Registrable Securities outstanding at the time of any such amendment,
        waiver or consent or thereafter shall be bound by any amendment, waiver
        or consent effected pursuant to this Section 7(b), whether or not any
        notice, writing or marking indicating such amendment, waiver or consent
        appears on the Registrable Securities or is delivered to such holder.

                (c)     Notices. All notices and other communications provided
        for or permitted hereunder shall be given as provided in the Purchase
        Agreement.

                (d)     Parties in Interest. The parties to this Agreement
        intend that all holders of Registrable Securities shall be entitled to
        receive the benefits of this Agreement and that any Electing Holder
        shall be bound by the terms and provisions of this Agreement by reason
        of such election with respect to the Registrable Securities which are
        included in a Shelf Registration Statement. All the terms and provisions
        of this Agreement shall be binding upon, shall inure to the benefit of
        and shall be enforceable by the respective successors and assigns of the
        parties hereto and any holder from time to time of the Registrable
        Securities to the aforesaid extent. In the event that any transferee of
        any holder of Registrable Securities shall acquire Registrable
        Securities, in any manner, whether by gift, bequest, purchase, operation
        of law or otherwise, such transferee shall, without any further writing
        or action of any kind, be entitled to receive the benefits of and, if an
        Electing Holder, be conclusively deemed to have agreed to be bound by
        and to perform all of the terms and provisions of this Agreement to the
        aforesaid extent.

                (e)     Counterparts. This Agreement may be executed in any
        number of counterparts and by the parties hereto in separate
        counterparts, each of which when so executed shall be deemed to be an
        original and all of which taken together shall constitute one and the
        same agreement.

                (f)     Headings. The headings in this agreement are for
        convenience of reference only and shall not limit or otherwise affect
        the meaning hereof.



                                       16
<PAGE>   17

                (g)     Governing Law. This Agreement shall be governed by and
        construed in accordance with the laws of the State of New York, without
        giving effect to any provisions relating to conflicts of laws.

                (h)     Severability. In the event that any one or more of the
        provisions contained herein, or the application thereof in any
        circumstances, is held invalid, illegal or unenforceable in any respect
        for any reason, the validity, legality and enforceability of any such
        provision in every other respect and of the remaining provisions hereof
        shall not be in any way impaired or affected thereby, it being intended
        that all of the rights and privileges of the parties hereto shall be
        enforceable to the fullest extent permitted by law.

                (i)     Survival. The respective indemnities, agreements,
        representations, warranties and other provisions set forth in this
        Agreement or made pursuant hereto shall remain in full force and effect,
        regardless of any investigation (or any statement as to the results
        thereof) made by or on behalf of any Electing Holder, any director,
        officer or partner of such holder, any agent or underwriter, any
        director, officer or partner of such agent or underwriter, or any
        controlling person of any of the foregoing, and shall survive the
        transfer and registration of the Registrable Securities of such holder.




                                       17
<PAGE>   18


                Please confirm that the foregoing correctly sets forth the
agreement between the Company and you.

                             Very truly yours,

                             XO Communications, Inc.



                             By:/s/ Gary D. Begeman
                                ---------------------------------
                                Name:  Gary D. Begeman
                                Title: Sr. Vice President and General Counsel

The foregoing Registration Rights Agreement is hereby confirmed and accepted as
of the date first above written.

Salomon Smith Barney Inc.
Goldman Sachs & Co.

By: /s/ A. Scott Daniel
   ---------------------------------
    Salomon Smith Barney Inc.
    On behalf of each of the Initial Purchasers




                                       18
<PAGE>   19


847709.2




                                                                       Exhibit A

                             XO Communications, Inc.

                         INSTRUCTION TO DTC PARTICIPANTS

                                (Date of Mailing)

                     URGENT - IMMEDIATE ATTENTION REQUESTED

                          DEADLINE FOR RESPONSE: [DATE]

               The Depository Trust Company ("DTC") has identified you as a DTC
Participant through which beneficial interests in the XO Communications, Inc.
(the "Company") 5 3/4% Convertible Subordinated Notes due 2009 (the "Convertible
Notes") and the shares of Class A Common Stock, par value $.02 per share (the
"Class A Common Stock"), issuable upon conversion thereof (together, the
"Securities") are held.

               The Company is in the process of registering the Securities under
the Securities Act of 1933 for resale by the beneficial owners thereof. In order
to have their Securities included in the registration statement, beneficial
owners must complete and return the enclosed Notice of Registration Statement
and Selling Security holder Questionnaire.

               It is important that beneficial owners of the Securities receive
a copy of the enclosed materials as soon as possible as their rights to have the
Securities included in the registration statement depend upon their returning
the Notice and Questionnaire by [DEADLINE FOR RESPONSE]. Please forward a copy
of the enclosed documents to each beneficial owner that holds interests in the
Securities through you. If you require more copies of the enclosed materials or
have any questions pertaining to this matter, please contact Salomon Smith
Barney Inc. General Counsel, 388 Greenwich Street, New York, NY 10013, telephone
no. _______________.




<PAGE>   20



                             XO Communications, Inc.

                        Notice of Registration Statement

                                       and

                      Selling Security holder Questionnaire

                                     (Date)

               Reference is hereby made to the Registration Rights Agreement
(the "Registration Rights Agreement") between XO Communications, Inc. (the
"Company") and the Initial Purchasers named therein. Pursuant to the
Registration Rights Agreement, the Company has filed with the United States
Securities and Exchange Commission (the "Commission") a registration statement
on Form S-3 (the "Shelf Registration Statement") for the registration and resale
under Rule 415 of the Securities Act of 1933, as amended (the "Securities Act"),
of the Company's 5 3/4% Convertible Subordinated Notes due 2009 (the
"Convertible Notes") and the shares of Class A Common Stock, par value $.02 per
share (the "Class A Common Stock"), issuable upon conversion thereof (together,
the "Securities"). A copy of the Registration Rights Agreement is attached
hereto. All capitalized terms not otherwise defined herein shall have the
meanings ascribed thereto in the Registration Rights Agreement.

               Each beneficial owner of Registrable Securities (as defined
below) is entitled to have the Registrable Securities beneficially owned by it
included in the Shelf Registration Statement. In order to have Registrable
Securities included in the Shelf Registration Statement, this Notice of
Registration Statement and Selling Security holder Questionnaire ("Notice and
Questionnaire") must be completed, executed and delivered to the Company's
counsel at the address set forth herein for receipt ON OR BEFORE [DEADLINE FOR
RESPONSE]. Beneficial owners of Registrable Securities who do not complete,
execute and return this Notice and Questionnaire by such date (i) will not be
named as selling securityholders in the Shelf Registration Statement and (ii)
may not use the Prospectus forming a part thereof for resales of Registrable
Securities.

               Certain legal consequences arise from being named as a selling
security holder in the Shelf Registration Statement and related Prospectus.
Accordingly, holders and beneficial owners of Registrable Securities are advised
to consult their own securities law counsel regarding the consequences of being
named or not being named as a selling security holder in the Shelf Registration
Statement and related Prospectus.

               The term "Registrable Securities" is defined in the Registration
Rights Agreement to mean all or any portion of the Convertible Subordinated
Notes and the shares of Class A Common Stock issuable upon conversion of such
Convertible Subordinated Notes and any common stock or securities of the Company
issued in exchange for or in respect of such common stock or securities, whether
as the result of any stock split or reclassification of, or stock dividend on,
such Common Stock or otherwise; provided, however, that a security ceases to be
a Registrable Security when it is no longer a Restricted Security.



                                      A-2
<PAGE>   21

               The term "Restricted Security" is defined in the Registration
Rights Agreement to mean any Convertible Subordinated Note or share of Class A
Common Stock issuable upon conversion thereof except any such Convertible
Subordinated Note or share of Class A Common Stock which (i) has been
effectively registered under the Securities Act and sold in a manner
contemplated by the Shelf Registration Statement, or (ii) has been transferred
in compliance with Rule 144 under the Securities Act (or any successor provision
thereto) or is transferable pursuant to paragraph (k) of such Rule 144 (or any
successor provision thereto), or (iii) has been sold in compliance with
Regulation S under the Securities Act (or any successor thereto).

                                    ELECTION

               The undersigned holder (the "Selling Security holder") of
Registrable Securities hereby elects to include in the Shelf Registration
Statement the Registrable Securities beneficially owned by it and listed below
in Item (3). The undersigned, by signing and returning this Notice and
Questionnaire, agrees to be bound with respect to such Registrable Securities by
the terms and conditions of this Notice and Questionnaire and the Registration
Rights Agreement, including, without limitation, Section 5 of the Registration
Rights Agreement, as if the undersigned Selling Security holder were an original
party thereto.

               The Selling Security holder hereby provides the following
information to the Company and represents and warrants that such information is
accurate and complete:




                                      A-3
<PAGE>   22


                                  QUESTIONNAIRE

(1)     (a)  Full Legal Name of Selling Security holder:


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

        (b)     Full Legal Name of Registered Holder (if not the same as in (a)
                above) of Registrable Securities Listed in (3) below:


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

        (c)     Full Legal Name of DTC Participant (if applicable and if not the
                same as (b) above) Through Which Registrable Securities Listed
                in (3) below are Held:


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


(2)     Address for Notices to Selling Security holder:

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

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

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

        Telephone:
                  --------------------------------------------------------------

        Fax:
            --------------------------------------------------------------------

        Contact Person:
                       ---------------------------------------------------------

(3)     Beneficial Ownership of Securities and shares of Class A Common Stock
        issued upon conversion of Securities:

               Except as set forth below in this Item (3), the undersigned does
not beneficially own any Securities or shares of Common Stock issued upon
conversion of any Securities.

        (a)     Principal amount of Registrable Securities (as defined in the
                Registration Rights Agreement) beneficially owned:
                                                                  --------------

                CUSIP No(s). of such Registrable Securities:
                                                            --------------------

                Number of shares of Class A Common Stock (if any) issued upon
                conversion of such Registrable Securities:
                                                          ----------------------

        (b)     Principal amount of Securities other than Registrable Securities
                beneficially owned:
                                   --------------------------------------------

                CUSIP No(s). of such other Securities:
                                                       ------------------------

                                      A-4
<PAGE>   23

               Number of shares of Class A Common Stock (if any) issued upon
               conversion of such other Securities:

        (c)    Principal amount of Registrable Securities which the undersigned
               wishes to be included in the Shelf Registration Statement:

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

               CUSIP No(s). of such Registrable Securities to be included in
               the Shelf Registration Statement:
                                                ------------------------------

               Number of shares of Class A Common Stock (if any) issued upon
               conversion of Registrable Securities which are to be included in
               the Shelf Registration Statement:
                                                -------------------------------

(4)     Beneficial Ownership of Other Securities of the Company:

               Except as set forth below in this Item (4), the undersigned
Selling Security holder is not the beneficial or registered owner of any shares
of Class A Common Stock or any other securities of the Company, other than the
Securities and shares of Class A Common Stock listed above in Item (3).

               State any exceptions here:



(5)     Relationships with the Company:

               Except as set forth below, neither the Selling Security holder
nor any of its affiliates, officers, directors or principal equity holders (5%
or more) has held any position or office or has had any other material
relationship with the Company (or its predecessors or affiliates) during the
past three years.

               State any exceptions here:

(6)     Plan of Distribution:

               Except as set forth below, the undersigned Selling Security
holder intends to distribute the Registrable Securities listed above in Item (3)
only as follows (if at all): Such Registrable Securities may be sold from time
to time directly by the undersigned Selling Security holder or, alternatively,
through underwriters, broker-dealers or agents. Such Registrable Securities may
be sold in one or more transactions at fixed prices, at prevailing market prices
at the time of sale, at varying prices determined at the time of sale, or at
negotiated prices. Such sales may be effected in transactions (which may involve
crosses or block transactions) (i) on any national securities exchange or
quotation service on which the Registered Securities may be listed or quoted at
the time of sale, (ii) in the over-the-counter market, (iii) in transactions
otherwise than on such exchanges or services or in the over-the-counter market,
or (iv) through the writing of options. In connection with sales of the

                                      A-5
<PAGE>   24

               Registrable Securities or otherwise, the Selling Security holder
may enter into hedging transactions with broker-dealers, which may in turn
engage in short sales of the Registrable Securities in the course of hedging the
positions they assume. The Selling Security holder may also sell Registrable
Securities short and deliver Registrable Securities to close out such short
positions, or loan or pledge Registrable Securities to broker-dealers that in
turn may sell such securities.

               State any exceptions here:

               Note:  In no event may such method(s) of distribution take the
form of an underwritten offering of the Registrable Securities without the prior
agreement of the Company.

               By signing below, the Selling Security holder acknowledges that
it understands its obligation to comply, and agrees that it will comply, with
the provisions of the Exchange Act and the rules and regulations thereunder,
particularly Regulation M.

               In the event that the Selling Security holder transfers all or
any portion of the Registrable Securities listed in Item (3) above after the
date on which such information is provided to the Company, the Selling Security
holder agrees to notify the transferee(s) at the time of the transfer of its
rights and obligations under this Notice and Questionnaire and the Registration
Rights Agreement.

               By signing below, the Selling Security holder consents to the
disclosure of the information contained herein in its answers to Items (1)
through (6) above and the inclusion of such information in the Shelf
Registration Statement and related Prospectus. The Selling Security holder
understands that such information will be relied upon by the Company in
connection with the preparation of the Shelf Registration Statement and related
Prospectus.

               In accordance with the Selling Security holder's obligation under
Section 3(a) of the Registration Rights Agreement to provide such information as
may be required by law for inclusion in the Shelf Registration Statement, the
Selling Security holder agrees to promptly notify the Company of any
inaccuracies or changes in the information provided herein which may occur
subsequent to the date hereof at any time while the Shelf Registration Statement
remains in effect. All notices hereunder and pursuant to the Registration Rights
Agreement shall be made in writing, by hand-delivery, first-class mail, or air
courier guaranteeing overnight delivery as follows:

               (i)    To the Company:

                      XO Communications, Inc.
                      1505 Farm Credit Drive
                      McLean, VA  22102

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<PAGE>   25

                (ii)  With a copy to:

                      Willkie Farr & Gallagher
                      787 Seventh Avenue
                      New York, NY  10019-6099
                      Attention:  Bruce R. Kraus

               Once this Notice and Questionnaire is executed by the Selling
Security holder and received by the Company's counsel, the terms of this Notice
and Questionnaire, and the representations and warranties contained herein,
shall be binding on, shall inure to the benefit of and shall be enforceable by
the respective successors, heirs, personal representatives, and assigns of the
Company and the Selling Security holder (with respect to the Registrable
Securities beneficially owned by such Selling Security holder and listed in Item
(3) above. This Agreement shall be governed in all respects by the laws of the
State of New York.




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<PAGE>   26


               IN WITNESS WHEREOF, the undersigned, by authority duly given, has
caused this Notice and Questionnaire to be executed and delivered either in
person or by its duly authorized agent.

Dated:  ________________

                             --------------------------------------------
                             Selling Security holder
                             (Print/type full legal name of beneficial
                             owner of Registrable Securities)





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

PLEASE RETURN THE COMPLETED AND EXECUTED NOTICE AND QUESTIONNAIRE FOR RECEIPT ON
OR BEFORE [DEADLINE FOR RESPONSE] TO THE COMPANY'S COUNSEL AT:

               Willkie Farr & Gallagher
               787 Seventh Avenue
               New York, NY  10019-6099
               Attention:  Bruce R. Kraus


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