Document:

<PAGE>   1
                                                                   EXHIBIT 10.15

                                 THIRD AMENDMENT

        THIRD AMENDMENT (this "Amendment") dated as of October 26, 1998 to the
Assumption Agreement and Amended and Restated Credit Agreement, dated as of
November 6, 1997 (as amended by the First Amendment thereto dated as of January
30, 1998 and by the Second Amendment thereto dated as of July 15, 1998 and as
may be further amended, supplemented or otherwise modified from time to time,
the "Credit Agreement"), among TransWestern Publishing Company LLC, a Delaware
limited liability company (the "Company"), TWP Capital Corp. II, a Delaware
corporation and a wholly owned Subsidiary of the Company ("TWP Capital II"; the
Company and TWP Capital II, collectively, the "Borrowers"), the several banks
and other financial institutions from time to time parties thereto (the
"Lenders"), Canadian Imperial Bank of Commerce, New York Agency, as
administrative agent for the Lenders thereunder (in such capacity, the
"Administrative Agent") and First Union National Bank, a national banking
association, as documentation agent for the Lenders thereunder (in such
capacity, the "Documentation Agent" and, together with the Administrative Agent,
the "Agents").

                              W I T N E S S E T H :

        WHEREAS, the Company has requested and the Administrative Agent and the
Required Lenders have agreed to amend certain provisions of the Credit Agreement
in the manner provided below;

        NOW, THEREFORE, in consideration of the premises and of the mutual
agreements herein contained, the parties hereto agree as follows:

        SECTION 1. Defined Terms. As used in this Amendment, unless otherwise
defined herein, terms defined in the Credit Agreement are used herein as therein
defined. Unless otherwise indicated, all Section and subsection references are
to the Credit Agreement.

        SECTION 2. Amendment. Subsection 7.10(f) of the Credit Agreement is
hereby amended by deleting in its entirety clause (i) of the proviso to said
subsection and replacing it with the following:

<PAGE>   2

                                                                              2

                "(i) except for (a) the acquisition by the Company from
        Universal Phone Books, Inc. of directories servicing certain areas in
        Michigan currently contemplated to occur in November 1998, the Total
        Amount Expended in connection with which shall not exceed $15,000,000
        and (ii) the acquisition by the Company from M&M Publishing, Inc. of
        directories servicing certain areas in Pennsylvania and New York
        currently contemplated to occur in November 1998, the Total Amount
        Expended with which shall not exceed $1,200,000, the Total Amount
        Expended in connection with all Permitted Acquisitions shall not exceed
        (x) in the aggregate in any fiscal year of the Company, $15,000,000 or
        (y) for any single Permitted Acquisition or series of related Permitted
        Acquisitions either (1) $7,5000,000, if the Total Leverage Ratio of the
        Company calculated after giving effect to the proposed Permitted
        Acquisition and the financing thereof is equal to or greater than 5.00
        to 1.00, or (2) $10,000,000, if the Total Leverage Ratio of the Company
        calculated after giving effect to the proposed Permitted Acquisition and
        the refinancing thereof is less than 5.00 to 1.00;"

        SECTION 4. Representations and Warranties. After giving effect to this
Amendment, the Borrowers hereby confirm, reaffirm and restate the
representations and warranties set forth in Section 3 of the Credit Agreement as
if made on and as of the date hereof.

        SECTION 5. Conditions to Effectiveness. This Amendment shall become
effective upon receipt by the Administrative Agent of counterparts of this
Amendment, duly executed and delivered by the Borrowers, Holdings and the
Required Lenders.

        SECTION 6. Miscellaneous. Except as expressly amended herein, the Credit
Agreement shall continue to be, and shall remain, in full force and effect in
accordance with its terms. This Amendment may be executed by the parties hereto
in any number of separate counterparts and all of said counterparts taken
together shall be deemed to constitute one and the same instrument. The Company
agrees to pay or reimburse the Administrative Agent for all its reasonable
out-of-pocket costs and expenses incurred in connection with the development,
preparation and execution of this Amendment including, without limitation, the
fees and disbursements of counsel to the Administrative Agent. THIS AMENDMENT
SHALL BE GOVERNED BY, AND CONSTRUED AND INTERPRETED IN ACCORDANCE WITH, THE LAWS
OF THE STATE OF NEW YORK.

<PAGE>   3

        IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed and delivered in New York, New York by their properly and duly
authorized officers as of the day and year first above written.

                                       TRANSWESTERN PUBLISHING COMPANY LLC

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

                                       TWP CAPITAL CORP. II

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

                                       TRANSWESTERN HOLDINGS L.P.

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

                                       CANADIAN IMPERIAL BANK OF COMMERCE,
                                       NEW YORK AGENCY,
                                       as Administrative Agent

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

                                       CIBC INC., as a Lender

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

<PAGE>   4

                                       FIRST UNION NATIONAL BANK,
                                       as Documentation Agent and as a Lender

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

                                       ARES LEVERAGED INVESTMENT FUND L.P.

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

                                       BANK OF HAWAII

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

                                       BANKBOSTON, N.A.

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

                                       BANKERS TRUST COMPANY

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

                                       FLEET NATIONAL BANK

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

<PAGE>   5

                                       ARCHIMEDES FUNDING, L.L.C.

                                       By: ING Capital Advisors, Inc.,
                                           as Collateral Manager

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

                                       PAM CAPITAL FUNDING L.P

                                       By: Highland Capital Management L.P.,
                                           as Collateral Manager

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

                                       KZH-CRESCENT CORPORATION

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

                                       CRESCENT/MACH I PARTNERS, L.P.

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

                                       VAN KAMPEN AMERICAN CAPITAL
                                       PRIME RATE INCOME TRUST

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

<PAGE>   6

                             VAN KAMPEN AMERICAN CAPITAL SENIOR
                             FLOATING RATE FUND

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

                             ALLIANCE INVESTMENT OPPORTUNITIES FUND, L.L.C.

                             By: Alliance Investment Opportunities Management,
                                 L.L.C., as Managing Member

                             By: Alliance Capital Management L.P.,
                                 as Managing Member

                             By: Alliance Capital Management Corporation,
                                 as General Partner

                             By:
                                -----------------------------------------------
                                Title:<PAGE>   1
                                                                   EXHIBIT 10.16

                                FOURTH AMENDMENT

        FOURTH AMENDMENT (this "Amendment") dated as of January 1, 1999 to the
Assumption Agreement and Amended and Restated Credit Agreement, dated as of
November 6, 1997 (as amended by the First Amendment thereto dated as of January
30, 1998, the Second Amendment thereto dated as of July 15, 1998, the Third
Amendment dated as of October 26, 1998 and as may be further amended,
supplemented or otherwise modified from time to time, the "Credit Agreement"),
among TransWestern Publishing Company LLC, a Delaware limited liability company
(the "Company"), TWP Capital Corp. II, a Delaware corporation and a wholly owned
Subsidiary of the Company ("TWP Capital II"; the Company and TWP Capital II,
collectively, the "Borrowers"), the several banks and other financial
institutions from time to time parties thereto (the "Lenders"), Canadian
Imperial Bank of Commerce, New York Agency, as administrative agent for the
Lenders thereunder (in such capacity, the "Administrative Agent") and First
Union National Bank, a national banking association, as documentation agent for
the Lenders thereunder (in such capacity, the "Documentation Agent" and,
together with the Administrative Agent, the "Agents").

                              W I T N E S S E T H :

        WHEREAS, the Company has requested and the Administrative Agent and the
Required Lenders have agreed to amend certain provisions of the Credit Agreement
in the manner provided below;

        NOW, THEREFORE, in consideration of the premises and of the mutual
agreements herein contained, the parties hereto agree as follows:

        SECTION 1. Defined Terms. As used in this Amendment, unless otherwise
defined herein, terms defined in the Credit Agreement are used herein as therein
defined. Unless otherwise indicated, all Section and subsection references are
to the Credit Agreement.

        SECTION 2. Amendment. Subsection 7.10(f) of the Credit Agreement is
hereby amended by deleting in its entirety clause (i) of the proviso to said
subsection and replacing it with the following:

<PAGE>   2

                                                                              2

                "(i) except for (a) the acquisition by the Company from
        Universal Phone Books, Inc. of directories servicing certain areas in
        Michigan on November , 1998, the Total Amount Expended in connection
        with which was $15,400,000 and (b) the acquisition by the Company from
        M&M Publishing, Inc. of directories servicing certain areas in
        Pennsylvania and New York on November 23, 1998, the Total Amount
        Expended with which was $1,200,000, the Total Amount Expended in
        connection with all Permitted Acquisitions shall not exceed in the
        aggregate in any fiscal year of the Company, $40,000,000, provided that
        after giving effect to such Permitted Acquisitions, no Default or Event
        of Default shall have occurred and be continuing."

        SECTION 4. Representations and Warranties. After giving effect to this
Amendment, the Borrowers hereby confirm, reaffirm and restate the
representations and warranties set forth in Section 3 of the Credit Agreement as
if made on and as of the date hereof.

        SECTION 5. Conditions to Effectiveness. This Amendment shall become
effective as of the date set forth above upon receipt by the Administrative
Agent of counterparts of this Amendment, duly executed and delivered by the
Borrowers, Holdings and the Required Lenders.

        SECTION 6. Miscellaneous. Except as expressly amended herein, the Credit
Agreement shall continue to be, and shall remain, in full force and effect in
accordance with its terms. This Amendment may be executed by the parties hereto
in any number of separate counterparts and all of said counterparts taken
together shall be deemed to constitute one and the same instrument. The Company
agrees to pay or reimburse the Administrative Agent for all its reasonable
out-of-pocket costs and expenses incurred in connection with the development,
preparation and execution of this Amendment including, without limitation, the
fees and disbursements of counsel to the Administrative Agent. THIS AMENDMENT
SHALL BE GOVERNED BY, AND CONSTRUED AND INTERPRETED IN ACCORDANCE WITH, THE LAWS
OF THE STATE OF NEW YORK.

<PAGE>   3

        IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed and delivered in New York, New York by their properly and duly
authorized officers as of the day and year first above written.

                                       TRANSWESTERN PUBLISHING COMPANY LLC

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

                                       TWP CAPITAL CORP. II

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

                                       TRANSWESTERN HOLDINGS L.P.

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

                                       CANADIAN IMPERIAL BANK OF COMMERCE,
                                       NEW YORK AGENCY, as Administrative Agent

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

                                       CIBC INC., as a Lender

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

<PAGE>   4

                                       FIRST UNION NATIONAL BANK,
                                       as Documentation Agent and as a Lender

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

                                       BANK OF HAWAII

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

                                       BANKBOSTON, N.A.

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

                                       BANKERS TRUST COMPANY

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

                                       FLEET NATIONAL BANK

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

<PAGE>   5

                                       ARCHIMEDES FUNDING, L.L.C.

                                       By: ING Capital Advisors, Inc.,
                                           as Collateral Manager

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

                                       PAM CAPITAL FUNDING L.P

                                       By: Highland Capital Management L.P.,
                                           as Collateral Manager

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

                                       KZH-CRESCENT CORPORATION

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

                                       CRESCENT/MACH I PARTNERS, L.P.

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

<PAGE>   6

                                       VAN KAMPEN AMERICAN CAPITAL
                                       PRIME RATE INCOME TRUST

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

                                       VAN KAMPEN AMERICAN CAPITAL SENIOR
                                       FLOATING RATE FUND

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

                                       ALLIANCE INVESTMENT OPPORTUNITIES FUND,
                                       L.L.C.

                                       By: Alliance Investment Opportunities
                                           Management, L.L.C.,
                                           as Managing Member

                                       By: Alliance Capital Management L.P.,
                                           as Managing Member

                                       By: Alliance Capital Management
                                           Corporation, as General Partner

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

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