Document:

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                                                                   EXHIBIT 10.14
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                              FIRST SUPPLEMENT TO

                             INTER-GROUP AGREEMENT

                               between and among

                                  AT&T CORP.,

                               on the one hand,

                                      and

                          LIBERTY MEDIA CORPORATION,

                            LIBERTY MEDIA GROUP LLC

                     and each Covered Entity listed on the

                            signature pages hereof,

                              on the other hand,

                           dated as of May 28, 1999

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                              FIRST SUPPLEMENT TO

                             INTER-GROUP AGREEMENT

          Agreement dated as of May 28, 1999 between AT&T Corp., a New York
corporation ("AT&T"), for itself and on behalf of the members of the Common
              ----
Stock Group, on the one hand, and Liberty Media Corporation, a Delaware
corporation ("LMC"), Liberty Media Group LLC, a Delaware limited liability
              ---
company, and for so long as such Covered Entity remains a Covered Entity under
the applicable provisions of the AT&T Charter Amendment, each Covered Entity
listed on the signature pages hereof (collectively, the "Liberty Media
                                                         -------------
Parties"), for themselves and, in the case of LMC, on behalf of the other
-------
members of the Liberty Media Group, on the other hand.  Capitalized terms used
herein without definition have the meanings ascribed to such terms in (i) the
AGI Merger Agreement (as hereinafter defined), (ii) if not otherwise defined
herein or in the AGI Merger Agreement, the Inter-Group Agreement (as hereinafter
defined) or (iii) with respect to Section 1.5, the Telewest Letter (as
hereinafter defined).

          WHEREAS, AT&T and the Liberty Media Parties are parties to that
certain Inter-Group Agreement (the "Inter-Group Agreement"), dated as of March
                                    ---------------------
9, 1999, which establishes certain terms and conditions concerning the
responsibilities and obligations of each Group to the other as well as certain
additional provisions concerning the Groups' relationships with each other;

          WHEREAS, AT&T, AGI Merger Sub, Inc., a Delaware corporation ("Merger
                                                                        ------
Sub"), LMC and The Associated Group, Inc., a Delaware corporation ("AGI"),
---                                                                 ---
intend to enter into an Agreement and Plan of Merger dated as of May 28, 1999
(the "AGI Merger Agreement") pursuant to which, among other things, subject to
      --------------------
the terms and conditions contained in the AGI Merger
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Agreement, Merger Sub will be merged with and into AGI and AGI, as the Surviving
Entity of such merger, will initially become a direct wholly owned subsidiary of
AT&T (the "AGI Merger");
           ---

          WHEREAS, certain members of the Liberty Media Group are negotiating a
form of letter (in the form approved in writing by AT&T, the "Telewest Letter")
to Microsoft Corporation ("Microsoft") relating to the interest currently held
by MediaOne Group, Inc. ("MediaOne") in Telewest that calls for the negotiation,
execution and delivery of certain agreements, instruments and other documents
that give effect to the arrangements described therein (collectively, and
including the obligations to which Microsoft would succeed pursuant to the
second paragraph of the Telewest Letter, but in each case only to the extent
approved in writing by AT&T, the "Microsoft/Telewest Arrangements");

          WHEREAS, in connection herewith AT&T, LMC and certain of their
respective affiliates are also entering into a First Amendment to Tax Sharing
Agreement (the "Tax Sharing Amendment"), dated as of the date hereof, which
amends that certain Tax Sharing Agreement, dated as of March 9, 1999 (as so
amended, the "Tax Sharing Agreement"), to which AT&T, LMC and certain of their
respective affiliates are parties;

          WHEREAS, as a condition to the willingness of each of AT&T and LMC to
enter into the AGI Merger Agreement and of the applicable members of the Liberty
Media Group to execute and deliver the Telewest Letter and the applicable
Microsoft/Telewest Arrangements, AT&T and the Liberty Media Parties have
determined to enter into this Agreement and the Tax Sharing Amendment;

          WHEREAS, AT&T and the Liberty Media Parties desire to supplement and
modify the Inter-Group Agreement in the manner set forth in this Agreement and
to establish in this Agreement certain terms and conditions concerning the
responsibilities and obligations of each Group

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to the other as well as certain additional provisions concerning each Group's
relationship with each other as the same may relate to the AGI Merger,
Microsoft/Telewest Arrangements and certain related transactions;

          WHEREAS, in connection herewith, the Capital Stock Committee has
adopted the resolutions attached as Exhibit A.

          NOW, THEREFORE, in consideration of the foregoing and the mutual
covenants and agreements contained herein, and intending to be legally bound
hereby, AT&T and the Liberty Media Parties hereby agree as follows:

                                   ARTICLE I

                    OBLIGATIONS RELATING TO THE AGI MERGER

          SECTION 1.1  Post-Closing Restructuring Steps.  To the extent not
                       --------------------------------
already accomplished pursuant to the AGI Merger Agreement, following the AGI
Merger but only if permitted by applicable law at such time, the Liberty Media
Group and the Common Stock Group shall take the actions and enter into the
transactions described in Exhibit 7.15 to the AGI Merger Agreement in the manner
and at the respective times described therein. Each of AT&T and LMC shall take,
and shall cause each of its respective Subsidiaries to take, any and all
required actions (whether as a stockholder (or other interest holder) or through
its respective representatives on the board of directors (or comparable
governing body) of the applicable entity), in the case of AT&T, only to the
extent specifically requested by LMC, to give effect to the previous sentence.
In the event that any of the actions or transactions described in Exhibit 7.15
to the AGI Merger Agreement are or become illegal or impossible to take or
complete under applicable law, the applicable members of the Common Stock Group
and the Liberty Media Group shall use their commercially reasonable

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efforts to take such other actions and/or complete such other transactions as
may be required so as to accomplish the respective intended results of and
benefits to the Common Stock Group and the Liberty Media Group from the actions
and transactions described in Exhibit B. From and after the taking of the action
described in paragraph 11 of such Exhibit 7.15, Silver Spur Land and Cattle
Company shall cause the Surviving Entity to comply with the Inter-Group
Agreement and the Tax Sharing Agreement.

          SECTION 1.2.  Certain Liabilities Relating to the AGI Merger.
                        ----------------------------------------------

          (a)  Subject to the last sentence of this subsection (a), as between
the Common Stock Group and the Liberty Media Group, all of the following
Liabilities shall be Liabilities of the Liberty Media Group:

          (i)  all Liabilities of AGI and any of its subsidiaries and affiliates
               (and, in each case, any predecessor or successor thereto);

          (ii) all Liabilities arising out of or related to the AGI Agreement
               and the transactions contemplated thereby, including (A) all
               Liabilities arising out of or relating to any breach of the AGI
               Merger Agreement by LMC or by AGI (whether such breach is of a
               representation, warranty, agreement or obligation made to Parent,
               LMC or otherwise, and without reference to any qualification of
               any such representation, warranty, agreement or obligation by
               reference to the Company SEC Reports or the Company Disclosure
               Schedule, and without reference to any limitation or survival of
               such representation, warranty, covenant or obligation set forth
               in the AGI Merger Agreement and without regard to Section 10.10
               of the AGI Merger Agreement), (B) any Liabilities

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                to third parties contemplated by Section 4.10 of the AGI Merger
                Agreement, (C) all Liabilities required to carry out the
                provisions of Section 2.1 of the AGI Merger Agreement, (D) all
                Liabilities under Sections 4.23 and 7.6 of the AGI Merger
                Agreement, and (E) all Liabilities arising out of or related to
                lawsuits brought, proposed or threatened by any third party
                (other than AGI) against AT&T or Merger Sub (a "Third Party
                Lawsuit") arising from the execution, delivery or performance of
                the AGI Merger Agreement or this Agreement (other than Section
                1.5) by AT&T or Merger Sub and (F) relieving AT&T and any member
                of the Common Stock Group of any Liability or obligation that
                binds or is enforceable against AT&T or such member of the
                Common Stock Group as a result of any agreement between AGI and
                its Subsidiaries, on the one hand, and any other person or
                entity (other than an agreement executed by AT&T or a member of
                the Common Stock Group), on the other hand;

          (iii) all Liabilities arising out of the consummation of the AGI
                Merger or any of the transactions contemplated thereby,
                including the Post-Merger Restructuring Transactions and any
                other transaction contemplated by this Agreement (other than
                Section 1.5) or the AGI Merger Agreement notwithstanding the
                failure to receive any consent, approval or authorization, or
                any failure to make any filing or notification, from or to any
                Person or Governmental Entity that may be required in connection
                therewith;

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          (iv)  all Liabilities arising out of or related to the consummation
                of, or failure to consummate, the Pre-Merger Restructuring
                Transactions or the Post-Merger Restructuring Transactions;

          (v)   all Liabilities relating to employees, officers, directors,
                consultants and other agents of AGI and any of its Subsidiaries
                and Affiliates, including, subject to subsection (e) below, all
                Liabilities contemplated by Sections 3.5, 3.6 and 3.7 of the AGI
                Merger Agreement and all Rollover Options and other Stock
                Incentives created pursuant to the AGI Merger Agreement; and

          (vi)  except to the extent resulting from any breach of this Agreement
                or the AGI Merger Agreement by AT&T that do not arise out of or
                relate to actions taken by AT&T at the request of LMC (as
                contemplated by Section 1.2(e) hereof or otherwise in writing),
                all Liabilities arising out of the execution, delivery or
                performance of this Agreement (other than Section 1.5).

Notwithstanding the foregoing, as between the Common Stock Group and the Liberty
Media Group, the Common Stock Group shall be responsible for (i) any Liabilities
(other than any Liability arising from or relating to a Clause D Tax Item (as
defined in the Tax Sharing Amendment)) to the extent arising out of or relating
to any breach by AT&T or Merger Sub of the AGI Merger Agreement or this
Agreement that do not arise out of or relate to actions taken by AT&T at the
request of LMC (as contemplated by Section 1.2(e) hereof or otherwise in
writing), whether incurred by a member of the Common Stock Group or by a member
of the Liberty Media Group, and (ii) any Clause D Tax Item (as defined in the
Tax Sharing Amendment), to the extent set forth in Section 3(d)(i) of the Tax
Sharing Agreement. No action taken, or failed to be taken, by the Surviving
Entity following the

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Effective Time shall be deemed to be a breach of this Agreement or the AGI
Merger Agreement by AT&T or Merger Sub unless Parent is required to cause the
Surviving Entity to take such action pursuant to Section 1.1 (provided, that in
no event shall AT&T or Merger Sub be deemed to have breached this Agreement or
the AGI Merger Agreement as a result of any action taken, or failed to be taken
by the Surviving Corporation as a result of any action taken, or failed to be
taken, by LMC or a member of the Liberty Media Group).

          (b)  The Liberty Media Group shall be responsible for, and shall
reimburse the Common Stock Group for, any and all reasonable costs, fees and
expenses incurred by AT&T or any member of the Common Stock Group in connection
with: (i) the negotiation, review, execution and delivery of the AGI Merger
Agreement and, the Tax Sharing Amendment; (ii) the consummation of the
transactions contemplated by the AGI Merger Agreement and this Agreement (other
than Section 1.5); (iii) the preparation, review and filing of the Registration
Statement (and the proxy statement that will be a part thereof); (iv) the
consummation of the Post-Merger Restructuring Transactions; (v) making any
filings with any Governmental Entity and otherwise assisting in obtaining
approvals, consents and clearances required in connection with the transactions
contemplated by the AGI Merger Agreement and this Agreement (other than Section
1.5), including any Facilitating Approval required in connection with the AGI
Merger; and (vi) all other fees and expenses related thereto, including in each
case any internal costs, fees and expenses (which shall be determined in any
reasonable manner developed by AT&T for tracking such internal costs, fees and
expenses), and in each case such costs, fees and expenses to be reimbursed
promptly upon receipt of a statement therefor.

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          (c)  LMC shall indemnify and hold harmless AT&T and each member of the
Common Stock Group from and against, and pay and reimburse AT&T and each member
of the Common Stock Group for, any and all Liabilities (including reasonable
attorneys' fees and expenses) for which the Liberty Media Group is responsible
pursuant to this Section 1.2 in each case in accordance with Section 1.4(c) of
the Inter-Group Agreement.

          (d)  LMC shall ensure that there is delivered to AT&T within five
business days of the Effective Time, and shall indemnify AT&T from and against
any loss or Liability arising from or related to the failure to be delivered to
AT&T (including as a member of the Common Stock Group) immediately following the
Effective Time, in each case free and clear of all Liens and Restrictions and
ready for cancellation, a number of shares of Parent Common Stock equal to the
Parent Common Stock Number.

          (e)  Notwithstanding any provision of the AGI Merger Agreement, AT&T
and Merger Sub shall not waive any condition to their respective obligations to
consummate the AGI Merger set forth in Article VIII of the AGI Merger Agreement
(the "Parent Closing Conditions") without LMC's prior written consent; provided,
      -------------------------
however, that consummation of the AGI Merger by Parent based on the reasonable
belief that all of the Parent Closing Conditions have been satisfied shall not
be deemed a breach of this Agreement unless (and to the extent) AT&T receives a
written request referred to in the next sentence at least 24 hours prior to the
then scheduled Closing of the AGI Merger.  To the extent so requested in writing
by LMC, each of Parent and Merger Sub shall (i) assert that one or more of the
Parent Closing Conditions have not been satisfied and decline to consummate the
transactions contemplated by the AGI Merger Agreement or (ii) waive one or more
of the Parent Closing Conditions (other than those set forth in Section 8.1 of
the AGI Merger

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Agreement). The Liberty Media Group agrees to indemnify AT&T for any Liabilities
incurred by AT&T or any member of the Common Stock Group as a result of the
taking of an action by AT&T or Merger Sub at the request of LMC as contemplated
by the previous sentence (but without regard to whether such action constitutes
a breach of the AGI Merger Agreement). Notwithstanding clause (ii) of the
previous sentence, AT&T shall not be obligated to waive any Parent Closing
Condition and consummate the AGI Merger if AT&T, in its reasonable judgment,
determines that the foregoing agreement of LMC to indemnify AT&T from and
against any Liability incurred as a result of such action is not adequate to
fully protect AT&T and the Common Stock Group from and against any Parent
Adverse Effect that could reasonably be expected to result from such waiver and
the consummation of the AGI Merger in connection therewith (it being understood
that no such indemnification would be adequate if such Parent Adverse Effect
relates to, without limitation, any injunction applicable to AT&T or any of its
Subsidiaries, any restriction on the operation of any business or assets of AT&T
or any of its Subsidiaries or the relationship of AT&T or any of its
Subsidiaries with any Governmental Entity that has jurisdiction over AT&T or
such Subsidiary or any of their assets or businesses. Except as set forth in
this paragraph, nothing herein shall prohibit AT&T or Merger Sub from exercising
any of its rights under the AGI Merger Agreement, including any right to refuse
to consummate the AGI Merger and any right to terminate the AGI Merger
Agreement, in each case in accordance with the terms of the AGI Merger
Agreement. AT&T shall reasonably consider any amendments to, or any waiver of
any other provision of, the AGI Merger Agreement proposed by LMC. If so
requested by AT&T, in connection with the closing of the AGI Merger, LMC shall
acknowledge in writing to AT&T that the consummation of the AGI Merger would not
be inconsistent with AT&T's obligations under this paragraph, and the failure of
AT&T

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to consummate the AGI Merger in the absence of such acknowledgment shall be
deemed, for all purposes of this Agreement, not to be a violation of this
Agreement or the AGI Merger Agreement.

          To the extent required in order to obtain any Facilitating Approval
necessary for the satisfaction of one or more of the Parent Closing Conditions
or to negate the effect of any Blocking Approval, LMC may, in its sole
discretion, elect to agree to one or more conditions, limitations or
restrictions regarding the conduct of its business or the ownership or operation
of its assets and businesses following the AGI Merger (including the businesses
and assets of AGI and its Subsidiaries), including any such condition,
limitation or restriction that may be imposed as a result of or in connection
with any Parent May Transaction, Parent Impeding Transaction or Munich Impeding
Transaction. In furtherance of the foregoing, in the event that AT&T elects to
delay the consummation of the AGI Merger pursuant to clause (ii) of Section
3.4(c) of the AGI Merger Agreement or delivers a Blocking Approval Notice, LMC,
may, in its sole discretion, take one or more of the actions described in the
previous sentence in order to prevent or eliminate the condition, event or
circumstance which is the basis for AT&T's election to delay the consummation of
the AGI Merger pursuant to clause (ii) of Section 3.4(c) of the AGI Merger
Agreement or to deliver a Blocking Approval Notice under clause (iv) of Section
3.4(c) of the AGI Merger Agreement.

          (f)  Subject to the condition that LMC shall have made available to
AT&T the amount(s) in cash required for AT&T to make the applicable payments,
AT&T shall make the cash payments required to be made by it or the Surviving
Entity in accordance with the terms and conditions of Sections 3.6(a) and 3.7 of
the AGI Merger Agreement at such times and in such amounts as may be directed by
LMC.  LMC shall take all actions necessary to require the Surviving Entity to
give effect to the foregoing sentence.

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          (g)  All employees, officers, directors, consultants and other agents
of AGI and its Subsidiaries shall be deemed to be employees, officers,
directors, consultants and other agents of the Liberty Media Group, and all
Stock Incentives that are created as a result of the AGI Merger shall be the
responsibility of the Liberty Media Group.

          (h)  For purposes of Section 1.16 of the Inter-Group Agreement, the
Rollover Options, the obligation to issue AT&T Liberty Tracking Shares to AGI
shareholders pursuant to the AGI Merger Agreement, and any other obligation to
issue or sell any AT&T Liberty Tracking Shares pursuant to or in connection with
the AGI Merger, the AGI Merger Agreement, and any agreement referred to in the
AGI Merger Agreement or executed in connection therewith shall be deemed to be
Tracking Stock Obligations incurred with a Liberty Approval. The issuance of
AT&T Liberty Tracking Shares and Rollover Options pursuant to the AGI Merger,
any Pre-Merger Restructuring Step, any Post-Merger Restructuring Step and any
other transaction contemplated by the AGI Merger Agreement shall be deemed to
have occurred with a Liberty Approval for purposes of Section 1.11(a) of the
Inter-Group Agreement and shall not be a breach of Section 1.11(b) or (c) of the
Inter-Group Agreement. Subject to Section 1.16 of the Inter-Group Agreement, any
action taken by Parent to implement the terms of this paragraph (h) or Section
3.7 of the AGI Merger Agreement shall not constitute a breach of any provision
of the Inter-Group Agreement.

          (i)  At all times from the date of its formation until the Effective
Time of the AGI Merger, Merger Sub shall be a Subsidiary of AT&T.

          SECTION 1.3.  Allocation of Proceeds. For purposes of Section 1.6(b)
                        ----------------------
of the Inter-Group Agreement and the definition of the term "Liberty Media
Group" in the AT&T Charter Amendment, (i) the net proceeds of the issuance of
the shares of Class A Munich Group Stock to be

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issued in the Merger shall consist of the entire interest of AT&T in the
Surviving Entity and each of its Subsidiaries (other than the shares of Parent
Common Stock held by AGI and its Subsidiaries at the time of the Merger referred
to in Exhibit B and any distributions on such shares that required an adjustment
pursuant to Section 2.5 of the AGI Merger Agreement), which shall be deemed to
represent the net proceeds of the issuance of the shares of Parent Common Stock
in the Merger), (ii) for purposes of clause (ii) of Section 1.6(b) of the Inter-
Group Agreement, the shares of Class A Munich Group Stock and Class B Munich
Group Stock held by AGI and its Subsidiaries at the time of the Merger shall be
deemed to have been acquired entirely with the shares of Class A Munich Group
Stock to be issued in the AGI Merger (provided, however, that Parent shall have
no obligation to LMC pursuant to Section 1.6(b) of the Inter-Group Agreement to
contribute such shares held by AGI and its Subsidiaries to LMC), and (iii) the
shares of Parent Common Stock and Class A Munich Group Stock issued upon
conversion of the shares Company Stock referred to in clause (b) of the
definition of the term "Liberty Media Group" in the AT&T Charter Amendment (and
the proceeds of any Disposition (as defined in the AT&T Charter Amendment)
thereof) shall remain attributed to the Liberty Media Group. Notwithstanding the
foregoing, if the foregoing allocation of proceeds would not be permitted under
the AT&T Charter Amendment, all of the assets acquired pursuant to the AGI
Merger Agreement shall be deemed to be part of the Liberty Media Group, except
that the shares of Parent Common Stock held by AGI and its Subsidiaries at the
time of the AGI Merger (and any distributions on such shares that required an
adjustment pursuant to Section 2.5 of the AGI Merger Agreement) shall be deemed
to have been transferred by the Liberty Media Group to the Common Stock Group in
respect of the agreement by AT&T to enter into this Agreement and issue an equal
number of shares of Parent Common Stock.

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          In furtherance of the foregoing, any contract right or other similar
right associated with any asset that is attributed to a Group in accordance with
the preceding paragraph shall be the right of the Group to which such related
asset is so attributed.

          SECTION 1.4.  Certain Obligations.
                        -------------------

          (a)  Section 3.4(c) and clause (I) of the proviso to the second
sentence of Section 3.4(a) of the AGI Merger Agreement are incorporated herein
in their entirety.

          (b)  Notwithstanding the foregoing, AT&T agrees to reasonably consider
any actions that it may be requested by LMC to take in accordance with
consummation of the AGI Merger.

          (c)  LMC represents and warrants that true and complete copies of all
documents referred to in the AGI Merger Agreement that have been delivered to
LMC by or on behalf of the Company on or prior to the date hereof have been
delivered to AT&T (or its counsel) on or prior to the date hereof and agrees
that true and complete copies of all such documents delivered to LMC from and
after the date hereof until consummation of the transactions contemplated hereby
will be delivered promptly to AT&T (or its counsel).

          SECTION 1.5.  Certain Liabilities Relating to the Microsoft/Telewest
                        ------------------------------------------------------
Arrangements.
------------

          (a)  As between the Common Stock Group and the Liberty Media Group,
all of the following Liabilities shall be Liabilities of the Common Stock Group:

          (i)  if the merger of MediaOne and AT&T or a subsidiary of AT&T (the
               "MediaOne Merger") occurs, all Liabilities of MediaOne and any
               predecessor or successor thereto relating to the interests in
               Telewest that are owned by

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               MediaOne and are transferred to Microsoft in connection with the
               Telewest Letter (the "Telewest Interests"); and

          (ii) all Liabilities arising out of or related to Liberty Media
               Group's execution and delivery of, or performance of its
               obligations under, the Telewest Letter and the Microsoft/Telewest
               Arrangements and the transactions contemplated thereby, including
               (A) all Liabilities arising out of or relating to any breach of
               the Microsoft/Telewest Arrangements by AT&T or any of its
               Subsidiaries or Affiliates and, if the MediaOne Merger occurs, by
               MediaOne or any of its Subsidiaries or Affiliates, (B) all
               Liabilities incurred by the Liberty Media Group required to carry
               out the provisions of Telewest Letter or the Microsoft/Telewest
               Arrangements (to the extent not reimbursed by Microsoft, provided
               that AT&T will be subrogated to the rights of the Liberty Media
               Group against Microsoft in such event), and (C) all Liabilities
               arising out of or related to lawsuits brought, proposed or
               threatened by any third party against LMC or a member of the
               Liberty Media Group (a "Third Party Lawsuit") arising from the
               execution, delivery or performance of the Telewest Letter or the
               Microsoft/Telewest Arrangements by LMC or any member of the
               Liberty Group (in any such case, without regard to the failure to
               receive any consent, approval or authorization, or any failure to
               make any filing or notification, from or to any Person or
               Governmental Entity that may be required in connection
               therewith).

                                      14
<PAGE>

Notwithstanding the foregoing, the Liberty Media Group shall be responsible for
any Liabilities to the extent arising out of or relating to any breach by a
member of the Liberty Media Group of the Telewest Letter or the
Microsoft/Telewest Arrangements that do not arise out of or relate to actions
taken by a member of the Liberty Media Group at the express written request of
AT&T, whether incurred by a member of the Common Stock Group or by a member of
the Liberty Media Group.

          (b)  The Common Stock Group shall be responsible for, and shall
reimburse the Liberty Media Group for, any and all reasonable costs, fees and
expenses incurred by LMC or any member of the Liberty Media Group in connection
with:  (i) the negotiation, review, execution and delivery of the Telewest
Letter and the Microsoft/Telewest Arrangements; (ii) the consummation of the
transactions contemplated by the Telewest Letter and the Microsoft/Telewest
Arrangements and this Agreement (with respect to the Microsoft Telewest
Arrangements); (iii) making any filings with any Governmental Entity and
otherwise assisting in obtaining approvals, consents and clearances required in
connection with the transactions contemplated by the Telewest Letter and the
Microsoft/Telewest Arrangements, including any Facilitating Approval required in
connection with the Microsoft/Telewest Arrangements; and (iv) all other
reasonable fees and expenses related thereto, including in each case any
reasonable internal costs, fees and expenses (which shall be determined in any
reasonable manner developed by LMC for tracking such internal costs, fees and
expenses), and in each case such costs, fees and expenses to be reimbursed
promptly upon receipt of a statement therefor; provided that, in each case (A)
LMC and the Liberty Media Group shall first seek such reimbursement from
Microsoft as provided in the Telewest Letter and (B) AT&T will be subrogated to
any rights of LMC and the Liberty Media Group against Microsoft with respect to
any payments made by AT&T pursuant to this Section 1.5.

                                      15
<PAGE>

          (c)  AT&T shall indemnify and hold harmless LMC and each member of the
Liberty Media Group from and against, and pay and reimburse LMC and each member
of the Liberty Media Group for, any all Liabilities (including reasonable
attorneys' fees and expenses) for which the Common Stock Group is responsible
pursuant to this Section 1.5 in each case in accordance with Section 1.4(c) of
the Inter-Group Agreement.

          (d)  Unless and then only to the extent otherwise required by a
"determination" (as defined in Section 1313(a)(1) of the Code) or by a similar
applicable provision of state or local income or franchise tax law, LMC agrees
(i) to report the transactions contemplated by the Telewest Letter and the
Microsoft/Telewest Arrangements as transactions not giving rise to income, gain
or loss for tax purposes and (ii) not to take any position in any audit,
administrative proceeding or litigation that is inconsistent with clause (i) of
this sentence.

                                  ARTICLE II

                                  DEFINITIONS

          SECTION 2.1.  Certain Defined Terms.  In addition to the terms defined
                        ---------------------
elsewhere in this Agreement, for purpose of this Agreement the following terms
shall have the following meanings:

          "Subsidiary" with respect to AGI, shall include Teligent and its
Subsidiaries and Portatel and its Subsidiaries.

          SECTION 2.2.  Other Definitional Provisions. The language used in this
                        -----------------------------
Agreement shall be deemed to be the language chosen by the parties to express
their mutual intent, and no rule of strict construction shall be applied against
any party. Any references to any statute or law shall also refer to all rules
and regulations promulgated thereunder, unless the context requires

                                      16
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otherwise. Whenever the context may require, any pronoun shall include the
corresponding masculine, feminine and neuter forms. The words "include,"
"includes," and "including" shall be deemed to be followed by the phrase
"without limitation". The words "hereof," "herein" and "hereunder" and words of
similar import when used in this Agreement shall refer to this Agreement as a
whole and not to any particular provision of this Agreement, and Article and
Section references are to this Agreement unless otherwise specified. The
meanings given to terms defined herein shall be equally applicable to both the
singular and plural forms of such terms. Unless the context shall otherwise
require, any references to any agreement or other instrument or statute or
regulation are to it as amended and supplemented from time to time (and, in the
case of a statute or regulation, to any successor provisions). Any reference in
this Agreement to a "day" or number of "days" (without the explicit
qualification of "business") shall be interpreted as a reference to a calendar
day or number of calendar days. If any action or notice is to be taken or given
on or by a particular calendar day, and such calendar day is not a business day,
then such action or notice shall be deferred until, or may be taken or given on,
the next business day.

                                  ARTICLE III

                                 MISCELLANEOUS

          SECTION 3.1.  Notices. All notices, requests, demands or other
                        -------
communications required by or otherwise with respect to this Agreement shall be
in writing and shall be deemed to have been given to any party when delivered
personally (by courier service or otherwise), when delivered by telecopy and
confirmed by return telecopy, or upon the receipt after being mailed by first-
class mail, postage prepaid and return receipt requested in each case to the
applicable addresses set forth below:

                                      17
<PAGE>

          If to AT&T or any member of the Common Stock Group:

               AT&T Corp.
               295 North Maple Avenue
               Basking Ridge, New Jersey  07920
               Attention: Vice President-Law
                          and Corporate Secretary
               Facsimile: (908) 221-6618

          with a copy to:

               Wachtell, Lipton, Rosen & Katz
               51 West 52nd Street
               New York, New York 10019
               Attention: Richard D. Katcher, Esq.
                          Steven A. Rosenblum, Esq.
               Facsimile: (212) 403-2000

          If to LMC or any member of the Liberty Media Group:

               Liberty Media Corporation
               9197 South Peoria Street
               Englewood, Colorado 80112
               Attention: Charles Y. Tanabe, Esq.
               Facsimile: (720) 875-5382

          with a copy to:

               Baker & Botts, L.L.P.
               599 Lexington Avenue
               New York, New York 10022
               Attention: Elizabeth M. Markowski, Esq.
                          John L. Graham, Esq.
               Facsimile: (212) 705-5125

or such address as such party shall have designated by notice so given to each
other party.

          SECTION 3.2.  Amendments; No Waivers.  (a) This Agreement shall be
                        ----------------------
amended, changed, supplemented, waived or otherwise modified only by an
instrument in writing signed by each of AT&T and LMC (and following a Triggering
Event, Liberty Media Group LLC).

                                      18
<PAGE>

          (b)  No failure or delay by any party in exercising any right, power
or privilege hereunder shall operate as a waiver thereof nor shall any single or
partial exercise thereof preclude any other or further exercise thereof or the
exercise of any other right, power or privilege. The rights and remedies herein
provided shall be cumulative and not exclusive of any rights or remedies
provided by law.

          SECTION 3.3.  Successors and Assigns.  Neither this Agreement nor any
                        ----------------------
of the rights or obligations under this Agreement shall be assigned, in whole or
in part, by any party without the prior written consent of the other parties
hereto; provided, however, that the assignment of its rights and obligations
        --------  -------
under this Agreement by LMC or any Covered Entity to Liberty Media Group LLC in
connection with the transactions contemplated by the Contribution Agreement
shall not require the consent of AT&T.  Subject to the foregoing, the provisions
of this Agreement shall be binding upon and inure to the benefit of the parties
hereto and their respective successors and assigns.

          SECTION 3.4.  Governing Law; Consent to Jurisdiction.  This Agreement
                        --------------------------------------
and all disputes hereunder shall be governed by and construed and enforced in
accordance with the internal laws of the State of Delaware, without regard to
the principles of conflicts of laws. Each party hereto irrevocably and
unconditionally consents to submit to the exclusive jurisdiction of the United
States District Court for the District of Delaware or the Chancery Court of the
State of Delaware in any action, suit or proceeding arising in connection with
this Agreement, and agrees that any such action, suit or proceeding shall be
brought only in such court (and waives any objection based on forum non
                                                              ----- ---
coveniens or any other objection to venue therein); provided, however, that such
---------                                           --------  -------
consent to jurisdiction is solely for the purpose referred to in this Section
4.4 and shall not be deemed to be a general submission to the jurisdiction of
said courts or of the State of Delaware other than for

                                      19
<PAGE>

such purpose. AT&T and LMC each hereby waive any right to a trial by jury in
connection with any such action, suit or proceeding.

          SECTION 3.5.  Counterparts; Effectiveness.  This Agreement may be
                        ---------------------------
executed in any number of counterparts, each of which shall be deemed to be an
original, but all of which together shall constitute one instrument. This
Agreement shall become effective when each party hereto shall have received
counterparts thereof signed by the other party hereto.

          SECTION 3.6.  Specific Performance.  Each of AT&T and LMC acknowledges
                        --------------------
and agrees that money damages are not an effective remedy for violations of this
Agreement and that any party may, in its sole discretion, apply to a court of
competent jurisdiction for specific performance or injunctive or such other
relief as such court may deem just and proper in order to enforce this Agreement
or prevent any violation hereof and, to the extent permitted by applicable Law,
each party waives any objection to the imposition of such relief.

          SECTION 3.7.  Remedies Cumulative.  All rights, powers and remedies
                        -------------------
provided under this Agreement or otherwise available in respect hereof at law or
in equity shall be cumulative and not alternative, and the exercise or beginning
of the exercise of any thereof by any party shall not preclude the simultaneous
or later exercise of any other such right, power or remedy by such party.

          SECTION 3.8.  Termination.  This Agreement shall remain in full force
                        -----------
and effect until the earlier to occur of (i) such time as no shares of Class A
Munich Group Stock or Class B Munich Group Stock are outstanding and (ii) the
termination of the AGI Merger Agreement, at which time this Agreement shall
terminate and upon termination, no party shall have any liability or further
obligation to the other under this Agreement except that the provisions of this
Section 3.8

                                      20
<PAGE>

shall survive the termination of this Agreement; provided, however, that such
termination shall not relieve any party hereto of any liability for any breach
of this Agreement or the AGI Merger Agreement. No termination of this Agreement
shall limit or otherwise affect the rights or obligations of the parties to the
Inter-Group Agreement.

          SECTION 3.9.  Severability.  In case any provision in this Agreement
                        ------------
shall be held invalid, illegal or unenforceable in a jurisdiction, such
provision shall be modified or deleted, as to the jurisdiction involved, only to
the extent necessary to render the same valid, legal and enforceable, and the
validity, legality and enforceability of the remaining provisions hereof shall
not in any way be affected or impaired thereby nor shall the validity, legality
or enforceability of such provision be affected thereby in any other
jurisdiction.

          SECTION 3.10. Cooperation.  Each of AT&T and LMC covenants and agrees
                        -----------
with the other to use its reasonable best efforts to cause each member of the
Common Stock Group and each member of the Liberty Media Group, respectively, to
fulfill each of its respective obligations under this Agreement.

                                      21
<PAGE>

          IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be duly executed as of the day and year first above written.

                              AT&T CORP.

                              By: /s/ Daniel E. Somers
                                  --------------------
                                  Name: Daniel E. Somers
                                  Title: Senior Executive Vice President and
                                         Chief Financial Officer

                              LIBERTY MEDIA CORPORATION

                              By: /s/ Gary S. Howard
                                  ------------------
                                  Name: Gary S. Howard
                                  Title: Executive Vice President and
                                         Chief Operating Officer

                              LIBERTY MEDIA GROUP LLC

                              By: /s/ Gary S. Howard
                                  ------------------
                                  Name: Gary S. Howard
                                  Title: Vice President
<PAGE>

                              Each of the following Covered Entities hereby
                              executes this Agreement as a member of the Liberty
                              Media Group to become a party to this Agreement
                              for so long as it remains a Covered Entity under
                              the applicable provisions of the AT&T Charter
                              Amendment:

                              TCIP, INC.

                              By: /s/ Gary S. Howard
                                  ------------------
                                  Name: Gary S. Howard
                                  Title:

                              SILVER SPUR LAND AND CATTLE CO.

                              By: /s/ Gary S. Howard
                                  ------------------
                                  Name: Gary S. Howard
                                  Title:

                              TCI INTERACTIVE, INC.

                              By: /s/ Gary S. Howard
                                  ------------------
                                  Name: Gary S. Howard
                                  Title:<PAGE>

                                                                   EXHIBIT 10.15
--------------------------------------------------------------------------------

                             SECOND SUPPLEMENT TO

                             INTER-GROUP AGREEMENT

                               between and among

                                  AT&T CORP.,

                               on the one hand,

                                      and

                          LIBERTY MEDIA CORPORATION,

                            LIBERTY MEDIA GROUP LLC

                     and each Covered Entity listed on the

                            signature pages hereof,

                              on the other hand,

                        dated as of September 24, 1999

--------------------------------------------------------------------------------
<PAGE>

                             SECOND SUPPLEMENT TO

                             INTER-GROUP AGREEMENT

          Agreement dated as of September 24, 1999 (this "Agreement") between
                                                          ---------
AT&T Corp., a New York corporation ("AT&T"), for itself and on behalf of the
                                     ----
members of the Common Stock Group, on the one hand, and Liberty Media
Corporation, a Delaware corporation ("LMC"), Liberty Media Group LLC, a Delaware
                                      ---
limited liability company, and for so long as such Covered Entity remains a
Covered Entity under the applicable provisions of the AT&T Charter Amendment,
each Covered Entity listed on the signature pages hereof (collectively, the
"Liberty Media Parties"), for themselves and, in the case of LMC, on behalf of
----------------------
the other members of the Liberty Media Group, on the other hand.  Capitalized
terms used herein without definition have the meanings ascribed to such terms in
the Inter-Group Agreement (as hereinafter defined).

          WHEREAS, AT&T and the Liberty Media Parties are parties to that
certain Inter-Group Agreement, dated as of March 9, 1999 (the "Inter-Group
                                                               -----------
Agreement"), as supplemented and modified by the First Supplement to Inter-Group
---------
Agreement, dated as of May 28, 1999 (the "First Supplement"), which establishes
                                          ----------------
certain terms and conditions concerning the responsibilities and obligations of
each Group to the other as well as certain additional provisions concerning the
Groups' relationships with each other;

          WHEREAS, in response to the request of the Liberty Media Parties, the
Capital Stock Committee of the AT&T Board of Directors has adopted the
resolutions attached as Exhibit A hereto approving and authorizing the
repurchase by AT&T from time to time of up to 135 million AT&T Liberty Tracking
Shares (as such number shall be adjusted from time to time to reflect stock
splits,
<PAGE>

stock dividends, stock combinations and similar events affecting the AT&T
Liberty Tracking Shares), in accordance with the terms and conditions set forth
in the resolution of the Capital Stock Committee and this Agreement (the "Stock
                                                                          -----
Repurchase Program"); and
------------------

          WHEREAS, AT&T and the Liberty Media Parties desire to supplement and
modify the Inter-Group Agreement in the manner set forth in this Agreement and
to establish in this Agreement certain terms and conditions concerning the
responsibilities and obligations of each Group to the other as well as certain
additional provisions concerning each Group's relationship with the other as the
same may relate to the Stock Repurchase Program and certain related
transactions.

          NOW, THEREFORE, in consideration of the foregoing and the mutual
covenants and agreements contained herein, and intending to be legally bound
hereby, AT&T and the Liberty Media Parties hereby agree as follows:

                                   ARTICLE I

     CERTAIN MATTERS RELATING TO THE STOCK REPURCHASE PROGRAM

          SECTION 1.1.  Repurchases of AT&T Liberty Tracking Shares.
                        -------------------------------------------

          (a)  Notwithstanding any provision of the Inter-Group Agreement to the
contrary, the Liberty Media Parties hereby consent (i) to the acquisition from
time to time of AT&T Liberty Tracking Shares by AT&T pursuant to the Stock
Repurchase Program, (ii) the use of funds, securities or other property
attributable to or to be made available by the Liberty Media Group to effect
such acquisitions and (iii) the consummation of any Repurchase Transaction in
accordance with the terms of any Repurchase Notice (as such terms are defined
herein).

          (b)  The Stock Repurchase Program will be effected through one or more
of the following methods, as specified by LMC (subject to Section 1.1(g) hereof)
in a Repurchase Notice

                                       2
<PAGE>

(as defined below) from time to time following the date hereof: (i) the purchase
by AT&T of AT&T Liberty Tracking Shares in open market transactions ("Open
                                                                      ----
Market Purchase Transactions"), (ii) the entering into by AT&T of agreements or
----------------------------
arrangements, or the issuance and sale by AT&T of securities or other
instruments, in each case giving any Person the right to require AT&T to
purchase a specified amount of AT&T Liberty Tracking Shares at a specified price
(any such agreement, arrangement or instrument, a "Put Right"), (iii) the
                                                   ---------
entering into by AT&T of agreements or arrangements with any Person granting to
AT&T the right to purchase a specified amount of AT&T Liberty Tracking Shares at
a specified price (such agreement or arrangement, a "Call Right") and (iv)
                                                     ----------
AT&T's engaging in swaps or other derivative transactions relating to the AT&T
Liberty Tracking Shares pursuant to which AT&T would directly or indirectly
acquire AT&T Liberty Tracking Shares. The creation of any Put Right, the
acquisition of any Call Right or the entering into of any other transaction
involving a swap or other derivative transaction described in clauses (ii),
(iii) and (iv) above are hereinafter referred to collectively as "Derivative
                                                                  ----------
Transactions", and Derivative Transactions and Open Market Purchase Transactions
------------
are hereinafter referred to collectively as "Repurchase Transactions".
                                             -----------------------

          (c)  LMC will notify AT&T in a writing signed by the President or any
Vice President of LMC (each, an "Authorized LMC Officer") of any proposed
                                 ----------------------
Repurchase Transaction, which notice shall specify the type of Repurchase
Transaction which LMC is requesting AT&T to engage in and include all material
terms and conditions thereof, including, without limitation, the amount of each
class of AT&T Liberty Tracking Shares to be acquired, the price or prices at
which such acquisitions should be consummated, the identity of any broker,
dealer or other securities professional to be utilized in connection with such
transaction, and the manner in which funds or

                                       3
<PAGE>

other property or securities owned by a member of the Liberty Media Group will
be made available to AT&T in connection with such transaction (such notice, a
"Repurchase Notice"). Such Repurchase Notice shall include a representation by
 -----------------
LMC to AT&T to the effect that there is no material nonpublic information
concerning the Liberty Media Parties and that consummation of the Repurchase
Transaction in the manner specified in the Repurchase Notice will comply with
applicable law. As to any Open Market Purchase Transaction, a Repurchase Notice
may be sent to AT&T contemporaneously with the placement of a purchase order on
behalf of AT&T by an Authorized LMC Officer with a broker, dealer or other
securities professional with whom AT&T has established an account at the request
of LMC (or in the event that AT&T has notified LMC that AT&T reasonably expects
to repurchase Common Stock on such day, with a broker designated by AT&T) for
the purpose of effecting Repurchase Transactions pursuant to this Agreement.

          (d)  Subject to Section 1.1(g) hereof, upon receipt of a Repurchase
Notice AT&T shall use its commercially reasonable efforts to effect the
requested transaction as promptly as practicable and in accordance with the
terms and conditions set forth in the Repurchase Notice and any applicable laws,
rules and regulations, including, but not limited to, federal and state
securities laws and the rules and regulations of The New York Stock Exchange,
Inc.  Unless otherwise consented to by AT&T, the parties agree that any Open
Market Purchase Transactions shall be made in accordance with Rule 10b-18
promulgated under the Securities Exchange Act of 1934, as amended, and any
successor rule or regulation or other applicable rule or regulation relating to
purchases by an issuer or its affiliate of the issuer's securities.

          (e)  In connection with any Repurchase Notice relating to a proposed
Derivative Transaction, AT&T shall not be required to engage in such Derivative
Transaction unless (i) the

                                       4
<PAGE>

period during which AT&T is obligated with respect to such Derivative
Transaction terminates no later than February 12, 2001 and (ii) following
discussions among the officers and employees of, and consultants and advisors
to, each of AT&T and LMC, as to the legal, tax, financial and accounting
implications of such proposed Derivative Transaction, AT&T and LMC, each acting
in good faith, shall have agreed that the proposed Derivative Transaction will
not result in or cause any significant negative impact upon AT&T or the Common
Stock Group, provided that any such agreement shall not prejudice AT&T's or the
Common Stock Group's rights under Section 1.2(b) hereof or under the Tax Sharing
Agreement among AT&T, LMC and the other parties thereto, as amended from time to
time (the "Tax Sharing Agreement").
           ---------------------

          (f)  In connection with any Repurchase Transaction, LMC shall make
available to the Common Stock Group such amount(s) in cash or, to the extent
that the Repurchase Transaction involves the payment by AT&T of consideration
other than cash, deliver such securities or other property as is required to
consummate the transaction contemplated by the Repurchase Notice, and, subject
to Section 1.1(g) hereof, AT&T shall make such cash payments or deliver such
securities or other property in connection with such transaction, all in
accordance with the terms specified in the Repurchase Notice; provided, however,
                                                              --------  -------
that in the event the Repurchase Transaction is not consummated for any reason
within the time period specified in such Repurchase Notice, AT&T shall so notify
LMC in writing of such event and, unless instructed in writing to the contrary
by LMC within two (2) Business Days of the date such notice is delivered, return
(i) to LMC any such cash, securities or other property that have been previously
delivered to AT&T and have not been delivered to a third party in accordance
with the terms of the Repurchase Notice or (ii) to the extent that such cash,
securities or other property have been delivered to a third party in accordance
with the terms

                                       5
<PAGE>

of the Repurchase Notice, use commercially reasonable efforts to require such
third party to deliver to AT&T (which will then be obligated to deliver such
cash, securities or other property to LMC) or LMC such cash, securities or other
property; provided, that to the extent AT&T is unable, through its use of
          --------
commercially reasonable efforts, to obtain the return of such cash, securities
or other property, AT&T shall assign any rights it may have with respect to such
cash, securities or other property (including any rights with respect to any
such third party) to LMC. In the case of a Repurchase Transaction effected in
accordance with the last sentence of Section 1.1(c), LMC shall make any such
payment or delivery to AT&T or, if so directed by AT&T, directly to the Person
specified in such Repurchase Notice, or if such Repurchase Notice contemplates
AT&T's establishment of an account for such purpose, to the account designated
by AT&T. All AT&T Liberty Tracking Shares acquired by AT&T pursuant to
Repurchase Transactions shall be cancelled and restored to the status of
authorized but unissued shares of the applicable class of AT&T Liberty Tracking
Shares.

          (g)  Notwithstanding anything to the contrary set forth in this
Agreement, AT&T shall not be required to effect a particular Repurchase
Transaction if (in each case, as reasonably determined by AT&T):

               (i)  at the time (x) the order is delivered to AT&T (or any
broker acting on its behalf) to purchase AT&T Liberty Tracking Shares in
connection with an Open Market Purchase Transaction, (y) AT&T (or any person
acting on its behalf) acquires the right to acquire AT&T Liberty Tracking Shares
from a third party in any Derivative Transaction or (z) that all parties to such
Repurchase Transaction have not irrevocably committed to consummate such
Repurchase Transaction, AT&T is or would be deemed to be in possession of
material nonpublic information

                                       6
<PAGE>

concerning the Liberty Media Parties or the AT&T Liberty Tracking Shares;
provided, however, that upon any such determination by it pursuant to this
--------  -------
Section 1(g)(i), AT&T shall promptly notify LMC of such determination and
thereafter AT&T's right to refuse to effect such Repurchase Transaction pursuant
to this Section 1(g)(i) shall terminate upon disclosure and dissemination (by
LMC or otherwise) of such material nonpublic information; provided, however,
                                                          --------  -------
that nothing herein shall require AT&T to make such disclosure.

               (ii)  consummation of such Repurchase Transaction would violate
any applicable law; or

               (iii) except with respect to Repurchase Transactions for which
orders with third parties have already been placed, AT&T notifies LMC that such
(or any) Repurchase Transaction would materially delay or interfere with a
potential merger, acquisition, sale of Common Stock, repurchase of Common Stock
or other transaction in which AT&T or the Common Stock Group intends to engage.

          SECTION 1.2.  Certain Liabilities Relating to the Stock Repurchase
                        ----------------------------------------------------
Program.
-------

          (a) Subject to the penultimate sentence of this subsection (a), the
Liberty Media Group shall be responsible for, and shall reimburse the Common
Stock Group for:  (i) any and all reasonable costs, fees and expenses incurred
by AT&T or any member of the Common Stock Group in connection with the
negotiation, review, execution and delivery of this Agreement and any agreement
required to be entered into by AT&T in connection with any Repurchase
Transaction; (ii) any and all costs, fees and expenses incurred by AT&T or any
member of the Common Stock Group directly in connection with the consummation of
any Repurchase Transaction entered into in accordance with this Agreement and
the applicable Repurchase Notice, including, without limitation,

                                       7
<PAGE>

any fees and expenses payable by AT&T to brokers, dealers or other securities
professionals or other advisors specified in any such Repurchase Notice (or to
the broker specified by AT&T pursuant to Section 1(c)) solely in connection with
any such Repurchase Transaction; (iii) any and all Liabilities (including
reasonable attorneys' fees and expenses) arising out of or resulting from any
action taken in good faith by AT&T or any member of the Common Stock Group in
accordance with this Agreement; and (iv) all other fees and expenses related to
AT&T's performance of its obligations hereunder relating to the Stock Repurchase
Program in accordance with the terms of this Agreement, including, in each case,
any internal costs, fees and expenses (which shall be determined in any
reasonable manner developed by AT&T for tracking such internal costs, fees and
expenses). All such costs, fees and expenses required to be reimbursed in
accordance with this Agreement shall be paid to AT&T promptly upon receipt of
appropriate documentation related thereto. Notwithstanding the foregoing, the
Common Stock Group will be liable for any Excluded Buyback Tax Items (as defined
in the amendment, dated the date hereof, to the Tax Sharing Agreement) to the
extent set forth in the Tax Sharing Agreement, as so amended. The Liberty Media
Group shall also be responsible for any and all costs, fees and expenses
incurred by any Liberty Media Party in connection herewith and any and all
Liabilities (including reasonable attorney's fees and expenses) arising out of
or resulting from any action taken by any Liberty Media Party in connection
herewith.

          (b)  LMC shall indemnify and hold harmless AT&T and each member of the
Common Stock Group from and against, and pay and reimburse AT&T and each member
of the Common Stock Group for, any and all Liabilities (including reasonable
attorneys' fees and expenses) (without duplication) for which the Liberty Media
Group is responsible pursuant to this Section 1.2 in each case in accordance
with Section 1.4(c) of the Inter-Group Agreement.  Any such Liability

                                       8
<PAGE>

shall be deemed to be a liability of the Liberty Media Group, as opposed to the
Common Stock Group, for all purposes hereunder and under the Inter-Group
Agreement.

          SECTION 1.3.  Debt Incurrence.  Any debt incurred, directly or
                        ---------------
indirectly, by AT&T or any member of the Common Stock Group in connection with
the acquisition, in compliance with this Agreement and the relevant Repurchase
Notice, of AT&T Liberty Tracking Shares pursuant to the Stock Repurchase Program
(i) shall constitute a Liberty Debt Incurrence, (ii) shall be deemed to be
incurred with a Liberty Approval and (iii) shall be included in total debt of
the Liberty Media Group for purposes of determining the Liberty Media Group Debt
Limit in accordance with Section 1.3(b) of the Inter-Group Agreement.

                                  ARTICLE II

                        REPRESENTATIONS AND WARRANTIES

          SECTION 2.1.  Representations and Warranties of AT&T.  AT&T represents
                        --------------------------------------
and warrant to LMC that (a) AT&T is a corporation duly organized, validly
existing and in good standing under the laws of the State of New York and has
the corporate power and authority to enter into this Agreement and to carry out
its obligations hereunder, (b) the execution and delivery of this Agreement by
AT&T and the consummation by AT&T of the transactions contemplated hereby have
been duly authorized by all necessary corporate action on the part of AT&T and
no other corporate proceedings on the part of AT&T are necessary to authorize
this Agreement or any of the transactions contemplated hereby, (c) this
Agreement has been duly executed and delivered by AT&T and constitutes a valid
and binding obligation of AT&T, and, assuming this Agreement constitutes a valid
and binding obligation of LMC and each of the Covered Entities, is enforceable
against AT&T

                                       9
<PAGE>

and each member of the Common Stock Group in accordance with its terms, (d)
neither the execution, delivery or performance of this Agreement by AT&T
constitutes a breach or violation of or conflicts with the AT&T Charter or
AT&T's By-Laws or any material agreement to which AT&T is a party, and (e) none
of such material agreements would impair in any material respect the ability of
AT&T to perform its obligations hereunder.

          SECTION 2.2.  Representations and Warranties of LMC. LMC represents
                        -------------------------------------
and warrants to AT&T that (a) LMC is a corporation duly organized, validly
existing and in good standing under the laws of Delaware and has the corporate
power and authority to enter into this Agreement and to carry out its
obligations hereunder, (b) the execution and delivery of this Agreement by LMC
and the consummation by LMC of the transactions contemplated hereby have been
duly authorized by all necessary action on the part of LMC and no other
proceedings on the part of LMC are necessary to authorize this Agreement or any
of the transactions contemplated hereby, (c) this Agreement has been duly
executed and delivered by LMC and each Covered Entity and constitutes a valid
and binding obligation of LMC and each Covered Entity, and, assuming this
Agreement constitutes a valid and binding obligation of AT&T, is enforceable
against LMC and each Covered Entity in accordance with its terms, (d) neither
the execution, delivery or performance of this Agreement by LMC constitutes a
breach or violation of or conflicts with its certificate of incorporation or by-
laws or any material agreement to which LMC is a party, (e) none of such
material agreements would impair in any material respect the ability of LMC to
perform its obligations hereunder and (f) this Agreement has been approved by a
Required Majority (as defined in LMC's Certificate of Incorporation) of the
members of the board of directors of LMC.

                                      10
<PAGE>

                                  ARTICLE III

                                 MISCELLANEOUS

          SECTION 3.1.  Notices. All notices, requests, demands or other
                        -------
communications required by or otherwise with respect to this Agreement shall be
in writing and shall be deemed to have been given to any party when delivered
personally (by courier service or otherwise), when delivered by telecopy and
confirmed by return telecopy, or upon the receipt after being mailed by first-
class mail, postage prepaid and return receipt requested in each case to the
applicable addresses or facsimile numbers set forth below:

     If to AT&T or any member of the Common Stock Group:

          AT&T Corp.
          295 North Maple Avenue
          Basking Ridge, New Jersey  07920
          Attention:   Vice President-Law
                       and Corporate Secretary
          Facsimile:   (908) 221-6618

     with a copy to:

          Wachtell, Lipton, Rosen & Katz
          51 West 52nd Street
          New York, New York 10019
          Attention:   Richard D. Katcher, Esq.
                       Steven A. Rosenblum, Esq.
          Facsimile:   (212) 403-2000

     If to LMC or any member of the Liberty Media Group:

          Liberty Media Corporation
          9197 South Peoria Street
          Englewood, Colorado 80112
          Attention:   Charles Y. Tanabe, Esq.
          Facsimile:   (720) 875-5382

                                      11
<PAGE>

     with a copy to:

          Baker & Botts, L.L.P.
          599 Lexington Avenue
          New York, New York 10022
          Attention:   Elizabeth M. Markowski, Esq.
          Facsimile:   (212) 705-5125

or such other address as such party shall have designated by notice so given to
each other party.

          SECTION 3.2.  Amendments; No Waivers.
                        ----------------------
          (a) This Agreement shall be amended, changed, supplemented, waived or
otherwise modified only by an instrument in writing signed by each of AT&T and
LMC (and following a Triggering Event, Liberty Media Group LLC).

          (b) No failure or delay by any party in exercising any right, power or
privilege hereunder shall operate as a waiver thereof nor shall any single or
partial exercise thereof preclude any other or further exercise thereof or the
exercise of any other right, power or privilege.  The rights and remedies herein
provided shall be cumulative and not exclusive of any rights or remedies
provided by law.

          SECTION 3.3.  Successors and Assigns. Neither this Agreement nor any
                        ----------------------
of the rights or obligations under this Agreement shall be assigned, in whole or
in part, by any party without the prior written consent of the other parties
hereto; provided, however, that the assignment of its rights and obligations
        --------  -------
under this Agreement by LMC or any Covered Entity to Liberty Media Group LLC in
connection with the transactions contemplated by the Contribution Agreement
shall not require the consent of AT&T. Subject to the foregoing, the provisions
of this Agreement shall be binding upon and inure to the benefit of the parties
hereto and their respective successors and assigns.

                                      12
<PAGE>

          SECTION 3.4.  Governing Law; Consent to Jurisdiction. This Agreement
                        --------------------------------------
and all disputes hereunder shall be governed by and construed and enforced in
accordance with the internal laws of the State of Delaware, without regard to
the principles of conflicts of laws. Each party hereto irrevocably and
unconditionally consents to submit to the exclusive jurisdiction of the United
States District Court for the District of Delaware or the Chancery Court of the
State of Delaware in any action, suit or proceeding arising in connection with
this Agreement, and agrees that any such action, suit or proceeding shall be
brought only in such court (and waives any objection based on forum non
                                                              ----- ---
coveniens or any other objection to venue therein); provided, however, that such
---------                                           --------  -------
consent to jurisdiction is solely for the purpose referred to in this Section
3.4 and shall not be deemed to be a general submission to the jurisdiction of
said courts or of the State of Delaware other than for such purpose.  AT&T and
LMC each hereby waive any right to a trial by jury in connection with any such
action, suit or proceeding.

          SECTION 3.5.  Counterparts; Effectiveness. This Agreement may be
                        ---------------------------
executed in any number of counterparts, each of which shall be deemed to be an
original, but all of which together shall constitute one instrument. This
Agreement shall become effective when each party hereto shall have received
counterparts hereof signed by the other parties hereto.

          SECTION 3.6.  Specific Performance. Each of AT&T and LMC acknowledges
                        --------------------
and agrees that money damages are not an effective remedy for violations of this
Agreement and that any party may, in its sole discretion, apply to a court of
competent jurisdiction for specific performance or injunctive or such other
relief as such court may deem just and proper in order to enforce this Agreement
or prevent any violation hereof and, to the extent permitted by applicable Law,
each party waives any objection to the imposition of such relief.

                                      13
<PAGE>

          SECTION 3.7.  Remedies Cumulative. All rights, powers and remedies
                        -------------------
provided under this Agreement or otherwise available in respect hereof at law or
in equity shall be cumulative and not alternative, and the exercise or beginning
of the exercise of any thereof by any party shall not preclude the simultaneous
or later exercise of any other such right, power or remedy by such party.

          SECTION 3.8.  Termination. This Agreement shall remain in full force
                        -----------
and effect until the Stock Repurchase Program has terminated and the parties
hereto have performed all of their respective obligations hereunder with respect
to Repurchase Transactions effected prior to such termination. The Stock
Repurchase Program will terminate when the maximum number of AT&T Liberty
Tracking Shares to be repurchased pursuant to the Stock Repurchase Program (as
such amount may be increased or decreased from time to time by action of the
Capital Stock Committee) shall have been reacquired by AT&T and cancelled and
restored to the status of authorized but unissued shares or, if applicable, at
such earlier date as of which (a) the Capital Stock Committee terminates or
cancels the Stock Repurchase Program, (b) the Stock Repurchase Program is
terminated by the Liberty Media Parties, as set forth in a public announcement
to such effect, or (c) there cease to be any AT&T Liberty Tracking Shares
outstanding. Upon termination of this Agreement, no party shall have any
liability or further obligation to the other under this Agreement, except that
the provisions of this Section 3.8 shall survive the termination of this
Agreement; provided, however, that such termination shall not relieve any party
           --------  -------
hereto of any liability (x) for any breach of this Agreement occurring prior to
such termination or (y) otherwise accrued hereunder. No termination of this
Agreement shall limit or otherwise affect the rights or obligations of the
parties to the Inter-Group Agreement or the Tax Sharing Agreement (as amended).

                                      14
<PAGE>

          SECTION 3.9.  Severability. In case any provision in this Agreement
                        ------------
shall be held invalid, illegal or unenforceable in a jurisdiction, such
provision shall be modified or deleted, as to the jurisdiction involved, only to
the extent necessary to render the same valid, legal and enforceable, and the
validity, legality and enforceability of the remaining provisions hereof shall
not in any way be affected or impaired thereby nor shall the validity, legality
or enforceability of such provision be affected thereby in any other
jurisdiction.

          SECTION 3.10. Cooperation. Each of AT&T and LMC covenants and agrees
                        -----------
with the other to use its reasonable best efforts to cause each member of the
Common Stock Group and each member of the Liberty Media Group, respectively, to
fulfill each of its respective obligations, if any, under this Agreement.

          SECTION 3.11. Interpretation. The language used in this Agreement
                        --------------
shall be deemed to be the language chosen by the parties to express their mutual
intent, and no rule of strict construction shall be applied against any party.
Any references to any statute or law shall also refer to all rules and
regulations promulgated thereunder, unless the context requires otherwise.
Whenever the context may require, any pronoun shall include the corresponding
masculine, feminine and neuter forms. The words "include," "includes," and
"including" shall be deemed to be followed by the phrase "without limitation".
The words "hereof," "herein" and "hereunder" and words of similar import when
used in this Agreement shall refer to this Agreement as a whole and not to any
particular provision of this Agreement, and Article and Section references are
to this Agreement unless otherwise specified. The meanings given to terms
defined herein shall be equally applicable to both the singular and plural forms
of such terms. Unless the context shall otherwise require, any references to any
agreement or other instrument or statute or regulation are to it as amended and
supplemented

                                      15
<PAGE>

from time to time (and, in the case of a statute or regulation, to any successor
provisions). Any reference in this Agreement to a "day" or number of "days"
(without the explicit qualification of "business") shall be interpreted as a
reference to a calendar day or number of calendar days. If any action or notice
is to be taken or given on or by a particular calendar day, and such calendar
day is not a business day, then such action or notice shall be deferred until,
or may be taken or given on, the next business day.

                                      16
<PAGE>

          IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be duly executed as of the day and year first above written.

                              AT&T CORP.

                              By: /s/ Marilyn J. Wasser
                                  ---------------------
                                  Name: Marilyn J. Wasser
                                  Title: Vice President--Law & Secretary

                              LIBERTY MEDIA CORPORATION

                              By: /s/ Gary S. Howard
                                  ------------------
                                  Name: Gary S. Howard
                                  Title: Executive Vice President

                              LIBERTY MEDIA GROUP LLC

                              By: /s/ Gary S. Howard
                                  ------------------
                                  Name: Gary S. Howard
                                  Title: Executive Vice President
<PAGE>

                              Each of the following Covered Entities hereby
                              executes this Agreement as a member of the Liberty
                              Media Group to become a party to this Agreement
                              for so long as it remains a Covered Entity under
                              the applicable provisions of the AT&T Charter
                              Amendment:

                              LIBERTY SP, INC.

                              By: /s/ Gary S. Howard
                                  ------------------
                                  Name: Gary S. Howard
                                  Title: Executive Vice President

                              LIBERTY AGI, INC.

                              By: /s/ Gary S. Howard
                                  ------------------
                                  Name: Gary S. Howard
                                  Title: Executive Vice President

                              LMC INTERACTIVE, INC.

                              By: /s/ Gary S. Howard
                                  ------------------
                                  Name: Gary S. Howard
                                  Title: Executive Vice President

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