<PAGE>

                              MEDIAONE GROUP, INC.

                          MEDIAONE GROUP FUNDING, INC.

                                       and


            WELLS FARGO BANK MINNESOTA, NATIONAL ASSOCIATION, Trustee




                          FIFTH SUPPLEMENTAL INDENTURE
                           Dated as of August 10, 2000



                Supplement to Indenture Dated as of June 12, 1998
                               as supplemented by
             First Supplemental Indenture Dated as of June 12, 1998,
            Second Supplemental Indenture Dated as of June 12, 1998,
         Third Supplemental Indenture Dated as of October 28, 1998, and
             Fourth Supplemental Indenture Dated as of June 15, 2000





              9.30% Subordinated Deferrable Interest Notes due 2025
              9.50% Subordinated Deferrable Interest Notes due 2036
              9.04% Subordinated Deferrable Interest Notes due 2038



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     FIFTH SUPPLEMENTAL INDENTURE, dated as of August 10, 2000 (this
"Supplemental Indenture"), is entered into by and among MediaOne Group, Inc., a
Delaware corporation (the "Company"), MediaOne Group Funding, Inc., a Delaware
corporation and indirect wholly owned subsidiary of the Company ("Funding"),
AT&T Corp., a New York corporation (the "Guarantor"), and Wells Fargo Bank
Minnesota, National Association, as trustee (the "Trustee").

     WHEREAS the Company is the successor guarantor under the Indenture, dated
as of June 12, 1998, as supplemented by a First Supplemental Indenture, dated as
of June 12, 1998, a Second Supplemental Indenture, dated as of June 12, 1998, a
Third Supplemental Indenture, dated as of October 28, 1998, and a Fourth
Supplemental Indenture, dated as of June __, 2000 (collectively, the "Original
Indenture", and together with this Supplemental Indenture, the "Indenture"),
pursuant to which Funding issued, and the Trustee authenticated and delivered
the following securities:

(a)  $274,240,825 aggregate principal amount of Funding's 9.30% Subordinated
     Deferrable Interest Notes due 2025 (the "Trust I Notes"); and

(b)  $219,595,100 aggregate principal amount of Funding's 9.50% Subordinated
     Deferrable Interest Notes due 2036 (the "Trust II Notes"); and

(c)  $515,463,925 aggregate principal amount of Funding's 9.04% Subordinated
     Deferrable Interest Notes due 2038 (the "Trust III Notes," and together
     with the Trust I Notes and the Trust II Notes, the "Subject Securities");

     WHEREAS MediaOne Finance Trust I, a Delaware statutory business trust
("Trust I"), has issued $266,452,700 aggregate liquidation amount of its 9.30%
Trust Originated Preferred Securities, representing undivided beneficial
interests in the assets of Trust I, and has invested the proceeds from such
issuance in the Trust I Notes;

     WHEREAS MediaOne Finance Trust II, a Delaware statutory business trust
("Trust II"), has issued $213,007,225 aggregate liquidation amount of its 9.50%
Trust Preferred Securities, representing undivided beneficial interests in the
assets of Trust II, and has invested the proceeds from such issuance in the
Trust II Notes;

     WHEREAS MediaOne Finance Trust III, a Delaware statutory business trust
("Trust III"), has issued $500,000,000 aggregate liquidation amount of its 9.04%
Trust Preferred Securities, representing undivided beneficial interests in the
assets of Trust III, and has invested the proceeds from such issuance in the
Trust III Notes;

     WHEREAS the Company is the successor guarantor and Funding is the obligor
with respect to the Subject Securities;

     WHEREAS the Guarantor desires to irrevocably and unconditionally guarantee,
on a subordinated basis, the full and punctual payment of principal of and
interest on the Subject Securities when due, whether at maturity, by
acceleration, by redemption or otherwise, and all other monetary obligations of
the Company and Funding under the Subject Securities and, with

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respect to the Subject Securities, under the Indenture (including obligations of
the Company and Funding to the Trustee), and the full and punctual performance
(within applicable grace periods) of all other obligations of the Company and
Funding under the Subject Securities and, with respect to the Subject
Securities, under the Indenture;

     WHEREAS the Company, Funding and the Guarantor have requested that the
Trustee execute and deliver this Supplemental Indenture and all requirements
necessary to make this Supplemental Indenture a valid instrument in accordance
with its terms and to make the guarantee provided for herein the valid
obligation of the Guarantor, and the execution and delivery of this Supplemental
Indenture have been duly authorized in all respects;

     NOW, THEREFORE, in consideration of the mutual promises contained herein
and for other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, the Company, Funding, the Guarantor and the
Trustee hereby agree as follows for the equal and ratable benefit of the Holders
of the Subject Securities:

     SECTION 1. DEFINITIONS.

     (a)  Capitalized terms used herein but not defined herein have the meanings
ascribed to such terms in the Original Indenture.

     (b)  Article I, Section 1.01, of the Original Indenture is hereby
supplemented, solely with respect to this Supplemental Indenture, to add the
following definitions:

          "Guarantor Senior Indebtedness" means all indebtedness, obligations or
     liabilities of the Guarantor, whether outstanding at the date of
     effectiveness of the Fifth Supplemental Indenture to the Indenture or
     thereafter incurred, assumed, guaranteed or otherwise created (including,
     without limitation, interest accruing on or after a bankruptcy or other
     similar event, whether or not an allowed claim therein), in respect of (A)
     indebtedness of the Guarantor for money borrowed, (B) indebtedness
     evidenced by securities, debentures, bonds, notes or other similar
     instruments issued by the Guarantor, (C) all capital lease obligations of
     the Guarantor, (D) all obligations of the Guarantor issued or assumed as
     the deferred purchase price of property, all conditional sale obligations
     of the Guarantor and all obligations of such obligor under any title
     retention agreement (but excluding trade accounts payable arising in the
     ordinary course of business), (E) all obligations of the Guarantor for
     reimbursement on any letter of credit, banker's acceptance, security
     purchase facility or similar credit transaction, (F) all obligations of the
     type referred to in clauses (A) through (E) of other Persons for the
     payment of which the Guarantor is responsible or liable as obligor,
     guarantor or otherwise, and (G) all obligations of the type referred to in
     clauses (A) through (F) of other Persons secured by any lien on any
     property or asset of the Guarantor (whether or not such obligation is
     assumed by such obligor), except for any such indebtedness, obligations or
     liabilities the terms of which expressly provide that such indebtedness,
     obligation or liability is equal or subordinated in right of payment to the
     Guarantor's guarantee with respect to the Subject Securities, as the case
     may be. For greater certainty, "Guarantor Senior Indebtedness" includes all
     indebtedness, obligations or liabilities

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     between or among the Guarantor and its Affiliates, except for such
     indebtedness, obligations or liabilities the terms of which expressly
     provide that such indebtedness, obligation or liability is equal or
     subordinated in right of payment to the Guarantor's guarantee with respect
     to the Subject Securities, as the case may be.

          "Guarantor Senior Indebtedness Representative" means any Person whom
     the Guarantor has, by written notice to the Trustee, identified as the
     indenture trustee or other trustee, agent or representative for an issue of
     Guarantor Senior Indebtedness.

     SECTION 2. GUARANTEE.

     (a)  The Guarantor irrevocably and unconditionally guarantees, on a
subordinated basis as set forth herein (the "Guarantee"), to each Holder of
Subject Securities and to the Trustee and its successors and assigns, (i) the
full and punctual payment of principal of and interest on the Subject Securities
when due, whether at maturity, by acceleration, by redemption or otherwise, and
all other monetary obligations of the Company and Funding with respect to the
Subject Securities under the Indenture (including obligations of the Company and
Funding to the Trustee) and the Subject Securities and (ii) the full and
punctual performance (within applicable grace periods) of all other obligations
of the Company and Funding with respect to the Subject Securities under the
Indenture and the Subject Securities.

     (b)  The Guarantor further agrees that the Guarantee constitutes a
guarantee of payment and performance and not of collection.

     (c)  The obligations of the Guarantor to make any payment hereunder may be
satisfied by causing the Company or Funding to make such payment.

     (d)  The Guarantor also agrees to pay any and all costs and expenses
(including reasonable attorneys fees) incurred by the Trustee or any Holder of
Subject Securities in enforcing any of their respective rights under the
Guarantee.

     SECTION 3. SUBORDINATION.

     The Guarantee is hereby expressly subordinated in right of payment, to the
extent and in the manner provided in this Supplemental Indenture, to the prior
payment in full in cash or cash equivalents of all Guarantor Senior Indebtedness
and such subordination is for the benefit of the holders of Guarantor Senior
Indebtedness. Upon any payment or distribution of all or substantially all the
assets of the Guarantor, whether voluntary or involuntary, or upon any
reorganization, readjustment, arrangement or similar proceeding relating to the
Guarantor or its property, whether or not the Guarantor is a party thereto and
whether in bankruptcy, insolvency, receivership or similar proceedings, or upon
any assignment by the Guarantor for the benefit of creditors or upon any other
marshaling of the assets and liabilities of the Guarantor:

          (i)  all Guarantor Senior Indebtedness shall first be paid in full in
     cash or cash equivalents, or provisions made for such payment by deposit
     thereof in trust with a bank or banks (either theretofore acting as
     trustees under indentures pursuant to which

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     Guarantor Senior Indebtedness shall have been issued or duly appointed
     paying agents for the purpose), before any payment is made in respect of
     the Guarantee;

          (ii) any payment in respect of the Guarantee to which the Holders of
     Subject Securities would be entitled except for the provisions of this
     Section shall be paid or delivered by the Guarantor or the liquidating
     trustee or agent or other Person making such payment, whether a trustee in
     bankruptcy, a receiver or liquidating trustee or other trustee or agent,
     directly and ratably to the holders of Guarantor Senior Indebtedness or the
     Guarantor Senior Indebtedness Representatives, as the case may be (subject
     to any subordination of any class of Guarantor Senior Indebtedness, by the
     provisions thereof, to any other class or classes of Guarantor Senior
     Indebtedness), according to the aggregate amounts remaining unpaid on
     account of the principal of; and the premium, if any, and interest on, and
     other monetary obligation with respect to, the Guarantor Senior
     Indebtedness, to the extent necessary to make payment in full of all
     Guarantor Senior Indebtedness remaining unpaid, after giving effect to any
     concurrent payment or distribution, or provision therefor, to the holders
     of such Guarantor Senior Indebtedness; and

          (iii) in the event that, notwithstanding the foregoing, any payment of
     any kind or character in respect of the Guarantee shall be received by the
     Trustee or the Holders of Subject Securities before all Guarantor Senior
     Indebtedness is paid in full, or provision made as aforesaid for its
     payment, such payment shall be held in trust for the ratable benefit of and
     shall be ratably paid over or delivered to the holders of Guarantor Senior
     Indebtedness remaining unpaid or unprovided for or the Guarantor Senior
     Indebtedness Representatives, as provided in the foregoing subparagraph
     (ii), for application to the payment of all principal of, and premium, if
     any, and interest on, and other monetary obligation with respect to, such
     Guarantor Senior Indebtedness remaining unpaid until all such Guarantor
     Senior Indebtedness shall have been paid in full, after giving effect to
     any concurrent payment or distribution, or provision therefor, to the
     holders of such Guarantor Senior Indebtedness.

     SECTION 4. DEFAULT ON GUARANTOR SENIOR INDEBTEDNESS.

     Subject to the provisions of Section 5, in the event and during the
continuation of any default in the payment of principal of, or premium, if any,
or interest on, or other monetary obligation with respect to, any Guarantor
Senior Indebtedness beyond any applicable period of grace, or in the event that
any event of default with respect to any Guarantor Senior Indebtedness shall
have occurred and be continuing, unless and until such default or event of
default shall have been cured or waived or shall have ceased to exist, no
payment shall be made by the Guarantor in respect of the Guarantee. Nothing
contained in this Section or elsewhere in this Supplemental Indenture shall,
however, prevent the application by the Trustee of any moneys deposited with it
hereunder by the Guarantor in respect of the Guarantee, if at the time of such
deposit, the Trustee did not have written notice of any event prohibiting the
making of such deposit by the Guarantor.

     The Guarantor shall give prompt written notice to the Trustee of any facts
that would prohibit the making of any payment of moneys in respect of the
Guarantee, including any

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dissolution, winding up, liquidation or reorganization of the Guarantor.
Anything in this Section or elsewhere in this Supplemental Indenture to the
contrary notwithstanding, the Trustee shall not be charged with knowledge of the
existence of any Guarantor Senior Indebtedness or of any default or event of
default with respect to any Guarantor Senior Indebtedness or of any other facts
that would prohibit the making of any payment of moneys hereunder, unless and
until the Trustee shall have received notice in writing to that effect signed by
an officer of the Guarantor or by a holder of Guarantor Senior Indebtedness who
shall have been certified by the Guarantor or otherwise established to the
reasonable satisfaction of the Trustee to be such holder or by a Guarantor
Senior Indebtedness Representative.

     SECTION 5. DISPUTES WITH HOLDERS OF CERTAIN GUARANTOR SENIOR INDEBTEDNESS.

     Any failure by the Guarantor to make any payment on or perform any other
obligation under Guarantor Senior Indebtedness, other than Guarantor Senior
Indebtedness consisting of any indebtedness incurred by the Guarantor or assumed
or guaranteed, directly or indirectly, by the Guarantor for money borrowed (or
any deferral, renewal, extension or refunding thereof) or consisting of any
indebtedness or obligation in which the provisions of this Section shall have
been waived by the Guarantor in the instrument or instruments by which the
Guarantor incurred, assumed, guaranteed or otherwise created such indebtedness
or obligation, shall not be deemed a default or event of default under Section 4
hereof for so long as (a) the Guarantor disputes its obligation to make such
payment or perform such obligation and (b) either (i) such dispute does not
result in a judgment against the Guarantor that remains undischarged, unbonded
or in force for more than the applicable appeal period or (ii) in the event of
such a judgment, the Guarantor in good faith prosecutes an appeal or other
proceeding for review and the Guarantor has obtained a stay of execution from
such judgment pending such appeal or review.

     SECTION 6. WHEN PAYMENT MUST BE PAID OVER

     If a payment is made pursuant to the Guarantee that because of Section 4 or
5 should not have been made to the Holders of the Subject Securities, the
Holders of Subject Securities who receive the payment shall hold it in trust for
holders of Guarantor Senior Indebtedness and pay it over to them as their
interests may appear.

     SECTION 7. RELATIVE RIGHTS.

     This Section defines the relative rights of Holders of Subject Securities
with respect to the Guarantee and holders of Guarantor Senior Indebtedness.
Nothing in this Indenture shall:

     (a)  impair, as between the Guarantor and Holders of Subject Securities,
the obligation of the Guarantor, which is absolute and unconditional, to make
payment under the Guarantee when, as and if due pursuant to this Supplemental
Indenture;

     (b)  affect the relative rights of Holders of Subject Securities and
creditors of the Guarantor other than holders of Guarantor Senior Indebtedness;
or

     (c)  prevent the Trustee or any Holder of Subject Securities from
exercising its available

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remedies with respect to the Guarantee, subject to the rights of holders of
Guarantor Senior Indebtedness to receive distributions otherwise payable to
Holders of Subject Securities.

     SECTION 8. SUBORDINATION MAY NOT BE IMPAIRED BY GUARANTOR.

     No right of any holder of Guarantor Senior Indebtedness to enforce the
subordination of the Guarantee shall be impaired by any act or failure to act by
the Guarantor or by its failure to comply with this Supplemental Indenture.

     SECTION 9. SEC REPORTS.

     The Guarantor shall file with the Trustee within 15 days after it files
them with the SEC copies of the annual reports and of the information, documents
and other reports (or copies of such portions of any of the foregoing as the SEC
may by rules and regulations prescribe) which the Guarantor is required to file
with the SEC pursuant to Section 13 or 15(d) of the Securities Exchange Act of
1934.

     SECTION 10. CONFLICT WITH THE TIA.

     If any provision of this Supplemental Indenture modifies or excludes any
provision of the TIA that is required under such Act to be part of and govern
the Indenture, the latter provision of the TIA shall control. If any provision
hereof modifies or excludes any provision of the TIA that may be so modified or
excluded, the latter provision of the TIA shall be deemed to apply to this
Supplemental Indenture, as so modified or excluded, as the case may be.

     SECTION 11. DATE AND TIME OF EFFECTIVENESS.

     This Supplemental Indenture shall become a legally effective and binding
instrument at and as of the date hereof.

     SECTION 12. SUPPLEMENTAL INDENTURE INCORPORATED INTO INDENTURE.

     The terms and conditions of this Supplemental Indenture shall be deemed to
be part of the Indenture for all purposes relating to the Subject Securities.
The Original Indenture, is hereby incorporated by reference herein and the
Original Indenture, as supplemented by this Supplemental Indenture, is in all
respects adopted, ratified and confirmed.

     SECTION 13. SUBJECT SECURITIES DEEMED CONFORMED.

     As of the date hereof, the provisions of the Subject Securities then
outstanding shall be deemed to be conformed, without the necessity for any
reissuance or exchange of such Subject Security or any other action on the part
of the Holders of Subject Securities, the Company, Funding or the Trustee, so as
to reflect this Supplemental Indenture.

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     SECTION 14. SUCCESSORS.

     All agreements of the Company, Funding, the Guarantor and the Trustee in
this Supplemental Indenture and in the Indenture shall bind their respective
successors.

     SECTION 15. BENEFITS OF SUPPLEMENTAL INDENTURE.

     Nothing in this Supplemental Indenture, express or implied, shall give to
any person, other than the parties hereto and their successors hereunder and the
Holders of Subject Securities, any benefit or any legal or equitable right,
remedy or claim under this Supplemental Indenture or the Indenture.

     SECTION 16. SEPARABILITY.

     In case any provision in this Supplemental Indenture, or in the Indenture,
shall be invalid, illegal or unenforceable, the validity, legality and
enforceability of the remaining provisions shall not in any way be affected or
impaired thereby, it being intended that all of the provisions hereof shall be
enforceable to the full extent permitted by law.

     SECTION 17. HEADINGS.

     The section headings of this Supplemental Indenture have been inserted for
convenience of reference only, are not to be considered a part of this
Supplemental Indenture and shall in no way modify or restrict any of the terms
or provisions hereof.

     SECTION 18. NOTICES.

     All notices provided for herein shall be in writing, duly signed by the
party giving such notice, and shall be delivered, telecopied or mailed by first
class mail as follows:

          (a)  if given to the Guarantor, to the Guarantor's mailing address set
forth below or such other address as the Guarantor may give notice of to the
Holders of the Subject Securities:

                           AT&T Corp.
                           32 Avenue of the Americas
                           New York, New York 10013-2412
                                   Attention: Legal Department;

          (b)  if given to the Trustee, to the address Set forth in the
Indenture or to such other address as the Trustee may give notice of to the
Holders of Subject Securities; and

          (c)  if given to any Holder of Subject Securities, at the address set
forth on the books and records of Trust I, Trust II or Trust III, as applicable.

     All such notices shall be deemed to have been given when received in
person, telecopied

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with receipt confirmed, or mailed by first class mail, postage prepaid except
that if a notice or other document is refused delivery or cannot be delivered
because of a changed address of which no notice was given, such notice or other
document shall be deemed to have been delivered on the date of such refusal or
inability to deliver.

     SECTION 19. GOVERNING LAW.

     THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED AND CONSTRUED IN ACCORDANCE
WITH THE INTERNAL LAWS OF THE STATE OF NEW YORK.

     SECTION 20. COUNTERPARTS.

     This Supplemental Indenture may be executed in two or more counterparts,
each of which shall constitute an original, but all of which when taken together
shall constitute the same instrument.

     SECTION 21. TRUSTEE NOT RESPONSIBLE FOR RECITALS.

     The recitals herein contained are made by the Company, Funding and the
Guarantor, and not by the Trustee, and the Trustee assumes no responsibility for
the correctness thereof. The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this Supplemental
Indenture.

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     IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed as of the date first above written.


                                       MEDIAONE GROUP, INC.

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



                                       MEDIAONE GROUP FUNDING, INC.

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



                                       AT&T CORP.

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



                                       WELLS FARGO BANK MINNESOTA,
                                       NATIONAL ASSOCIATION, as Trustee

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


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