<PAGE>   1
                                                                  EXHIBIT 10.4.3


                       AMENDMENT NO. 3 TO CREDIT AGREEMENT

                  AMENDMENT NO. 3, dated as of March 31, 2001 (this "Amendment")
to Credit Agreement, by and among Private Business, Inc., a Tennessee
corporation (the "Borrower"), the Lenders and Fleet National Bank, as the
Initial Issuing Bank, the Swing Line Bank and the Administrative Agent.

                             PRELIMINARY STATEMENTS

                  (A)      The Borrower, the Lenders, Fleet National Bank, as
the Initial Issuing Bank, the Swing Line Bank and the Administrative Agent, and
BankBoston N.A., as Syndication Agent, are parties to the Credit Agreement,
dated as of August 7, 1998 (as amended to the date hereof, the "Credit
Agreement").

                  (B)      The Borrower has requested that the Lenders amend the
Credit Agreement as more fully set forth below.

                  (C)      The Administrative Agent and the Lenders are willing
to amend the Credit Agreement on the terms and conditions set forth herein.

                  (D)      The terms defined in the Credit Agreement and not
otherwise defined herein shall have the meanings ascribed to them in the Credit
Agreement.

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

ARTICLE 1.        Amendments to Credit Agreement.

         Section 1.1       Amendment. This Amendment shall be deemed to be an
amendment to the Credit Agreement and shall not be construed in any way as a
replacement or substitution therefor. All of the terms and conditions of, and
terms defined in, this Amendment are hereby incorporated by reference into the
Credit Agreement as if such terms and provisions were set forth in full therein.

         Section 1.2       Amendments to Credit Agreement. Effective upon the
satisfaction of the conditions precedent set forth in Article 4 hereof, the
Credit Agreement is hereby amended as follows:

                  (a)      The aggregate amount of the Revolving Credit
Commitments are reduced from $15,000,000 to $10,000,000. The Revolving Credit
Commitment of each Revolving Credit Lender shall be reduced pro rata such that
the new Revolving Credit Commitment of each Revolving Credit Lender shall be as
set forth below:
<PAGE>   2

<TABLE>
<CAPTION>
                  Revolving Credit Lender              Revolving Credit Commitment
                  -----------------------              ---------------------------
                  <S>                                  <C>
                  Fleet National Bank                         $4,545,454.57

                  Citizens Bank of Massachusetts              $2,727,272.73

                  LaSalle Bank National Association           $1,818,181.82

                  Credit Lyonnais New York Branch             $  909,090.91
</TABLE>

                  (b)      Section 1.1 is amended by deleting from the
definition of "Applicable Margin" the tables entitled "Applicable Margin for
Eurodollar Rate Advances" and "Applicable Margin for Prime Rate Advances" and
replacing them with the following tables:

                 Applicable Margin for Eurodollar Rate Advances

<TABLE>
<CAPTION>
Ratio of Consolidated               Revolving Credit Advances,
Debt to EBITDA                      Term A Advances                    Term B Advances
---------------------               --------------------------         ---------------
<S>                                 <C>                                <C>
Greater than 3.00                            3.50%                           4.00%

Greater than 2.50
 less than or equal to 3.00                  3.00%                           3.50%

Greater than 2.00
 less than or equal to 2.50                  2.75%                           3.25%

Less than or equal to 2.00                   2.50%                           3.25%
</TABLE>

                    Applicable Margin for Prime Rate Advances

<TABLE>
<CAPTION>
Ratio of Consolidated               Revolving Credit Advances,
Debt to EBITDA                      Term A Advances                    Term B Advances
---------------------               --------------------------         ---------------
<S>                                 <C>                                <C>
Greater than 3.00                            2.25%                           2.75%

Greater than 2.50
 less than or equal to 3.00                  1.75%                           2.25%

Greater than 2.00
 less than or equal to 2.50                  1.50%                           2.25%

Less than or equal to 2.00                   1.25%                           2.25%
</TABLE>

                  (c)      Section 2.6(b)(i) is amended by deleting such Section
in its entirety and replacing it with the following:

                  "Within ninety (90) days following the end of each Fiscal Year
in which the Ratio of Consolidated Debt to EBITDA at the end of such Fiscal Year
exceeds 2.00:1, the Borrower shall execute and deliver to the Administrative
Agent a certificate of the Borrower's Chief Executive Officer or Chief Financial
Officer demonstrating its calculation of Excess Cash Flow


                                      -2-
<PAGE>   3

for such Fiscal Year along with a prepayment of the then outstanding Advances
equal to seventy-five percent (75%) of the annual Excess Cash Flow; provided,
however, that if the Ratio of the Consolidated Debt to EBITDA, measured at the
end of such Fiscal Year of the Borrower, for such Fiscal Year of the Borrower,
is equal to or less than 2.00:1, then there shall be no required prepayment out
of annual Excess Cash Flow for such Fiscal Year."

                  (d)      Section 8.1 is amended by deleting the minimum EBITDA
covenant levels for the period ending on or about March 31, 2001 and all periods
thereafter and replacing them with the following:

<TABLE>
<CAPTION>
         Four Fiscal Quarters ending on or about:             Minimum EBITDA
         ----------------------------------------             --------------
         <S>                                                  <C>
         March 31, 2001                                       $15,000,000
         June 30, 2001                                        $15,250,000
         September 30, 2001                                   $15,500,000
         December 31, 2001                                    $15,750,000

         March 31, 2002                                       $16,000,000
         June 30, 2002                                        $16,500,000
         September 30, 2002                                   $16,500,000
         December 31, 2002                                    $16,700,000

         March 31, 2003                                       $17,750,000
         June 30, 2003                                        $17,750,000
         September 30, 2003                                   $17,750,000
         December 31, 2003                                    $18,000,000

         March 31, 2004                                       $18,750,000
         June 30, 2004                                        $18,750,000
         September 30, 2004                                   $19,000,000
         December 31, 2004                                    $19,000,000

         March 31, 2005                                       $19,500,000
         June 30, 2005                                        $20,000,000
         September 30, 2005                                   $20,000,000
         December 31, 2005                                    $21,000,000

         March 31, 2006 and thereafter                        $22,000,000
</TABLE>

                  (c)      Section 8.2 is amended by deleting the maximum Ratio
of Consolidated Debt to EBITDA covenant levels for the period ending on or about
March 31, 2001 and all periods thereafter and replacing them with the following:


                                      -3-
<PAGE>   4

<TABLE>
<CAPTION>
         Four Fiscal Quarters ending on or about:             Ratio
         ----------------------------------------             ------
         <S>                                                  <C>
         March 31, 2001                                       3.25:1
         June 30, 2001                                        3.00:1
         September 30, 2001                                   2.75:1
         December 31, 2001                                    2.50:1

         March 31, 2002                                       2.50:1
         June 30, 2002                                        2.25:1
         September 30, 2002                                   2.25:1
         December 31, 2002                                    2.00:1

         March 31, 2003                                       2.00:1
         June 30, 2003                                        1.75:1
         September 30, 2003                                   1.75:1
         December 31, 2003                                    1.75:1

         March 31, 2004                                       1.75:1
         June 30, 2004 and thereafter                         1.50:1
</TABLE>

                  (d)      Section 8.3 is amended by deleting the minimum
Interest Coverage Ratio covenant levels for the period ending on or about March
31, 2001 and all periods thereafter and replacing them with the following:

<TABLE>
<CAPTION>
         Four Fiscal Quarters ending on or about:             Ratio
         ----------------------------------------             ------
         <S>                                                  <C>
         March 31, 2001                                       3.00:1
         June 30, 2001                                        3.25:1
         September 30, 2001                                   3.25:1
         December 31, 2001                                    3.50:1

         March 31, 2002                                       3.50:1
         June 30, 2002                                        3.75:1
         September 30, 2002                                   4.00:1
         December 31, 2002 and thereafter                     4.50:1
</TABLE>

                  (e)      Section 8.4 is amended by deleting the minimum Fixed
Charge Coverage Ratio covenant levels for the period ending on or about March
31, 2001 and all periods thereafter and replacing them with the following:

<TABLE>
<CAPTION>
         Four Fiscal Quarters ending on or about:             Ratio
         ----------------------------------------             ------
         <S>                                                  <C>
         March 31, 2001                                       1.10:1
         June 30, 2001                                        1.15:1
         September 30, 2001                                   1.25:1
         December 31, 2001                                    1.25:1

         March 31, 2002                                       1.25:1
         June 30, 2002                                        1.25:1
         September 30, 2002                                   1.25:1
         December 31, 2002                                    1.25:1

         March 31, 2003                                       1.25:1
         June 30, 2003                                        1.25:1
         September 30, 2003                                   1.25:1
         December 31, 2003                                    1.25:1

         March 31, 2004                                       1.25:1
         June 30, 2004                                        1.25:1
         September 30, 2004                                   1.25:1
         December 31, 2004                                    1.25:1

         March 31, 2005                                       1.00:1
         June 30, 2005                                        1.00:1
         September 30, 2005                                   1.00:1
         December 31, 2005                                    1.00:1

         March 31, 2006 and thereafter                        1.25:1
</TABLE>


                                      -4-
<PAGE>   5

ARTICLE 2.        Confirmations and References.

         Section 2.1       Continuing Effect. The Credit Agreement and the other
Loan Documents delivered in connection therewith are, and shall continue to be,
in full force and effect, and are hereby ratified and confirmed in all respects
except that on and after the date hereof:

                  (a)      All references in the Credit Agreement and all
                           references in the other Loan Documents:

                           (i)      to the "Credit Agreement," "thereto,"
"thereof," "thereunder" or words of like import referring to the Credit
Agreement shall mean the Credit Agreement as amended hereby; and

                           (ii)     to the "Loan Documents" shall be deemed to
include this Amendment.

                  (b)      All references in the Credit Agreement to "this
Agreement," "hereto," "hereof," "hereunder" or words of like import referring to
the Credit Agreement shall mean the Credit Agreement as amended hereby.

         Section 2.2       Confirmation of Liens. The Liens granted pursuant to
the Collateral Documents secure, without limitation, the Obligations of the
Borrower and its Subsidiaries to the Lenders and the Administrative Agent under
the Credit Agreement as amended by this Amendment. The term "Obligations" as
used in the Collateral Documents (or any other term used therein to refer to the
liabilities and obligations of the Borrower and its Subsidiaries to the Lenders
and the Administrative Agent), include, without limitation, Obligations to the
Lenders and the Administrative Agent under the Credit Agreement as amended by
this Amendment.

ARTICLE 3.        Representations and Warranties.

         The Borrower and each Loan Party hereby represents and warrants to the
Lenders and the Administrative Agent that:


                                      -5-
<PAGE>   6

         Section 3.1       Existing Representations. Each of the representations
and warranties contained in Article 4 of the Credit Agreement is true in all
material respects on, and as though made as of, the date hereof, other than any
such representation or warranty that, by its terms, refers to a specific date,
in which case, as of such specific date.

         Section 3.2       No Default. As of the date hereof, there exists no
Default or Event of Default under the Credit Agreement, as amended hereby, and
no event which, with the giving of notice or lapse of time, or both, would
constitute a Default or Event of Default.

         Section 3.3       Power, Authority, Consents. The Borrower has the
power to execute, deliver and perform the Credit Agreement, as amended by this
Amendment. The Borrower has taken all necessary action to authorize the
execution, delivery and performance of this Amendment. No consent or approval of
any Person, no consent or approval of any landlord or mortgagee, no waiver of
any lien or right of distraint or other similar right and no consent, license,
approval, authorization or declaration of any governmental authority, bureau or
agency, is required in connection with the execution, delivery or performance by
the Borrower or the validity, enforcement or priority, of this Amendment.

         Section 3.4       No Violation of Law or Agreements. The execution and
delivery by the Borrower of this Amendment and performance by it hereunder, will
not violate any provision of law presently in effect and will not conflict with
or result in a breach of any order, writ, injunction, ordinance, resolution,
decree, or other similar document or instrument presently in effect of any court
or governmental authority, bureau or agency, domestic or foreign, or the
certificate of incorporation or by-laws of the Borrower, or create (with or
without the giving of notice or lapse of time, or both) a default under or
breach of any agreement, bond, note or indenture presently in effect to which
the Borrower is a party, or by which it is bound or any of its properties or
assets is affected, or result in the imposition of any Lien of any nature
whatsoever upon any of the properties or assets owned by or used in connection
with the business of the Borrower, except for the Liens created and granted
pursuant to the Collateral Documents as acknowledged and confirmed herein.

         Section 3.5       Binding Effect. This Amendment has been duly executed
and delivered by the Borrower and constitutes the valid and legally binding
obligation of the Borrower, except as such enforceability may be limited by
applicable bankruptcy, insolvency, reorganization, moratorium or other similar
laws, now or hereafter in effect, relating to or affecting the enforcement of
creditors' rights generally, and except that the remedy of specific performance
and other equitable remedies are subject to judicial discretion.

ARTICLE 4.        Conditions to Amendment.

         The effectiveness of the amendments contained in Article 1 shall be
subject to the fulfillment of the following conditions precedent:

         Section 4.1       Amendment. The Borrower, the Required Lenders and
Revolving Credit Lenders holding greater than 50% of the aggregate Revolving
Credit Commitments shall have executed and delivered to the Administrative Agent
this Amendment.

         Section 4.2       No Default. There shall exist no Event of Default or
Default under the Credit Agreement.


                                      -6-
<PAGE>   7

         Section 4.3       Representations and Warranties. The representations
and warranties contained in Article 3 hereof shall be true and correct in all
material respects on the date hereof..

         Section 4.4       Amendment Fee. The Borrower shall have paid an
amendment fee to the Administrative Agent, for the account of each Lender which
has approved this Amendment, as evidenced by such Lender's timely execution and
delivery of a counterpart signature page to this Amendment, in an amount equal
to 0.25% (i.e. 25 basis points) of the aggregate of such approving Lenders'
Commitments immediately after the effectiveness of this Amendment.

ARTICLE 5.        Miscellaneous.

         Section 5.1       Continued Effectiveness. Except as specifically
amended herein, the Credit Agreement and each of the other Loan Documents shall
remain in full force and effect in accordance with their respective terms.

         Section 5.2       Governing Law. This Amendment shall be governed and
construed in accordance with the laws of the State of New York.

         Section 5.3       Severability. The provisions of this Amendment are
severable, and if any clause or provision shall be held invalid or unenforceable
in whole or in part in any jurisdiction, then such invalidity or
unenforceability shall affect only such clause or provision, or part thereof, in
such jurisdiction and shall not in any manner affect such clause or provision in
any other jurisdiction, or any other clause or provision in this Amendment in
any jurisdiction.

         Section 5.4       Counterparts. This Amendment may be signed in any
number of counterparts with the same effect as if the signatures thereto and
hereto were upon the same instrument. Delivery of an executed counterpart of
this Amendment by facsimile shall be as effective as delivery of an originally
executed counterpart.

         Section 5.5       Binding Effect; Assignment. This Amendment shall be
binding upon and inure to the benefit of the Borrower and its respective
successors and to the benefit of the Administrative Agent and the Lenders and
their respective successors and assigns. The rights and obligations of the
Borrower under this Amendment shall not be assigned or delegated without the
prior written consent of the Lenders, and any purported assignment or delegation
without such consent shall be void.

         Section 5.6       Expenses. The Borrower shall pay the Administrative
Agent upon demand for all reasonable expenses, including reasonable fees of
counsel for the Administrative Agent, incurred by the Administrative Agent in
connection with the preparation, negotiation and execution of this Amendment and
any documents required to be furnished herewith.

                            [Signature Pages Follow]


                                      -7-
<PAGE>   8

                  IN WITNESS WHEREOF, the parties hereto have caused this
Amendment to be executed by their respective officers thereunto duly authorized
on the date first above written.

                                      PRIVATE BUSINESS, INC.,
                                      AS BORROWER



                                      By:            /s/ Fred P. Read
                                             ----------------------------------

                                      Title:     Chief Financial Officer
                                             ----------------------------------


 [SIGNATURE PAGE TO PRIVATE BUSINESS, INC. AMENDMENT NO. 3 TO CREDIT AGREEMENT]
<PAGE>   9

                                      FLEET NATIONAL BANK,
                                      AS INITIAL ISSUING BANK,
                                      AS SWING LINE BANK,
                                      AS ADMINISTRATIVE AGENT AND
                                      AS LENDER


                                      By:            /s/ Paul Holian
                                             ----------------------------------

                                      Title:         Vice President
                                             ----------------------------------


 [SIGNATURE PAGE TO PRIVATE BUSINESS, INC. AMENDMENT NO. 3 TO CREDIT AGREEMENT]
<PAGE>   10

                                      CITIZENS BANK OF MASSACHUSETTS,
                                      AS LENDER



                                      By:
                                            -----------------------------------

                                      Title:
                                            -----------------------------------


 [SIGNATURE PAGE TO PRIVATE BUSINESS, INC. AMENDMENT NO. 3 TO CREDIT AGREEMENT]
<PAGE>   11

                                     PILGRIM PRIME RATE TRUST,
                                     AS LENDER

                                     By: Pilgrim Investments, Inc.,
                                     as its Investment Manager



                                     By:           /s/ Michel Prince
                                            -----------------------------------
                                     Title:          Vice President
                                            -----------------------------------

 [SIGNATURE PAGE TO PRIVATE BUSINESS, INC. AMENDMENT NO. 3 TO CREDIT AGREEMENT]
<PAGE>   12

                                     LASALLE BANK NATIONAL ASSOCIATION,
                                     AS LENDER



                                     By:          /s/ Todd Kostelnik
                                            -----------------------------------

                                     Title:       First Vice President
                                            -----------------------------------

 [SIGNATURE PAGE TO PRIVATE BUSINESS, INC. AMENDMENT NO. 3 TO CREDIT AGREEMENT]
<PAGE>   13

                                     CREDIT LYONNAIS NEW YORK BRANCH,
                                     AS LENDER



                                     By:            /s/ Mischa Zabotin
                                            -----------------------------------

                                     Title:        First Vice President
                                            -----------------------------------

 [SIGNATURE PAGE TO PRIVATE BUSINESS, INC. AMENDMENT NO. 3 TO CREDIT AGREEMENT]