Document:

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                                                                  EXHIBIT 10.2.7

                             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 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.

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        "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, 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");

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        (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 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

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        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) (1) 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.

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

            (3) 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

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        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:

            (1) when the Shelf Registration Statement and any amendment thereto
            has been filed with the Commission and when the Shelf Registration
            Statement or any post-effective amendment thereto has become
            effective;

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

            (3) 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;

            (4) 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

            (5) 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.

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            (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 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.

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

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            (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
            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;

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            (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 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

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        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.

        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

                                      -10-
<PAGE>   11

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 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

                                      -11-
<PAGE>   12

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.

        (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 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.

                                      -12-
<PAGE>   13

        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 33
1/3% 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.

                                      -13-
<PAGE>   14

        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 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.

                                      -14-
<PAGE>   15

        (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.

                                      -15-
<PAGE>   16

        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: Senior Vice President, General
                                             Counsel and Secretary

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/ Scott Daniels
        ---------------------------------------------
        Salomon Smith Barney Inc.
        On behalf of each of the Initial Purchasers

                                      -16-
<PAGE>   17

                                                                       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>   18

                           A-9 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.

                                      A-2
<PAGE>   19

            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.

            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>   20

                                         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:
                               -------------------------------------------------

                                      A-4
<PAGE>   21

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

            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>   22

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:

                                      A-6
<PAGE>   23

            (i)   To the Company:

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

            (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.

                                      A-7
<PAGE>   24

        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

                                      A-8Executed in 6 Parts
                                                             Counterpart No. ( )

                            NATIONAL EQUITY TRUST

                           TOP TEN PORTFOLIO SERIES 28

                           REFERENCE TRUST AGREEMENT

     This Reference Trust Agreement dated ________, 2001 among Prudential
Securities Incorporated, as Depositor and The Bank of New York, as Trustee, sets
forth certain provisions in full and incorporates other provisions by reference
to the document entitled "National Equity Trust, Trust Indenture and Agreement"
(the "Basic Agreement") dated February 2, 2000. Such provisions as are set forth
in full herein and such provisions as are incorporated by reference constitute a
single instrument (the "Indenture").

                                WITNESSETH THAT:

     In consideration of the premises and of the mutual agreements herein
contained, the Depositor and the Trustee agree as follows: Part I.

                     STANDARD TERMS AND CONDITIONS OF TRUST

     Subject to the provisions of Part II hereof, all the provisions contained
in the Basic Agreement are herein incorporated by reference in their entirety
and shall be deemed to be a part of this instrument as fully and to the same
extent as though said provisions had been set forth in full in this instrument.

A.      Article III, entitled "Administration of Trust," shall be amended as
        follows:

        (i)  Section 3.14 Deferred Sales Charge shall be amended to add the
             following sentences at the end thereof:

             "References to Deferred Sales Charge in this Trust Indenture and
             Agreement shall include any Creation and Development Fee indicated
             in the prospectus for a Trust.  The Creation and Development Fee
             shall be payable on each date so designated and in an amount
             determined as specified in the prospectus for a Trust."

<PAGE>
                                    Part II.

                     SPECIAL TERMS AND CONDITIONS OF TRUST

     The following special terms and conditions are hereby agreed to:

A.   The Trust is denominated National Equity Trust, Top Ten Portfolio Series
     28.

B.   The Units of the Trust shall be subject to a deferred sales charge.

C.   The publicly traded stocks listed in Schedule A hereto are those which,
     subject to the terms of this Indenture, have been or are to be deposited in
     Trust under this Indenture as of the date hereof.

D.   The term "Depositor" shall mean Prudential Securities Incorporated.

E.   The aggregate number of Units referred to in Sections 2.03 and 9.01 of the
      Basic Agreement is          as of the date hereof.

F.   A Unit of the Trust is hereby declared initially equal to 1/     th of the
     Trust.

G.   The term "First Settlement Date" shall mean                        , 2001.

H.   The terms "Computation Day" and "Record Date" shall mean          2001,
                  2001,            2001 and                 2001.

I.   The term "Distribution Date" shall mean            2001,           2001,
                  2001 and            2001.

J.   The term "Termination Date" shall mean          , 2001.

K.   The Trustee's Annual Fee shall be $      (per 1,000 Units) for 49,999,999
     and below units outstanding $      (per 1,000 Units) on the next 50,000,000
     Units, $     (per 1,000 Units) on the next 100,000,000 Units and $     (per
     1,000 Units) on Units in excess of 200,000,000 Units.  In calculating the
     Trustee's annual fee, the fee applicable to the number of units outstanding
     shall apply to all units outstanding.

L.   The Depositor's Portfolio supervisory service fee shall be $     per 1,000
     Units.

               [Signatures and acknowledgments on separate pages]

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