Document:

<PAGE>   1

                                                                     EXHIBIT 4.3

                           CERTIFICATE OF ELIMINATION

                                       OF

                    SERIES C $20 CONVERTIBLE PREFERRED STOCK

                                       OF

                        INTEGRATED SECURITY SYSTEMS, INC.

                       (Pursuant to Section 151(g) of the
                        Delaware General Corporation Law)

                  Integrated Security Systems, Inc., a corporation organized and
existing under the General Corporation Law of the State of Delaware (the
"Corporation") does hereby certify that the following resolutions respecting
Series C $20 Convertible Preferred Stock were duly adopted by the Corporation's
Board of Directors:

                           RESOLVED, that no shares of the Corporation's Series
                  C $20 Convertible Preferred Stock are outstanding and that no
                  shares of the Series C $20 Convertible Preferred Stock will be
                  issued subject to the certificate of designation previously
                  filed with respect to the Series C $20 Convertible Preferred
                  Stock; and

                           FURTHER RESOLVED, that the officers of the
                  Corporation are directed to file with the Secretary of State
                  of the State of Delaware a certificate pursuant to Section
                  151(g) of the General Corporation Law of the State of Delaware
                  setting forth these resolutions in order to eliminate from the
                  Corporation's certificate of incorporation all matters set
                  forth in the certificate of designation with respect to the
                  Series C $20 Convertible Preferred Stock.

                  In witness whereof, the Corporation has caused this
Certificate to be signed by its duly authorized officer this 14th day of March,
2001.
                                  INTEGRATED SECURITY SYSTEMS, INC.

                                  By:  /s/ C.A. RUNDELL, JR.
                                     ------------------------------------------
                                      C.A. Rundell, Jr., Chief Executive Officer<PAGE>   1
                                                                   EXHIBIT 10.72

                       AMENDMENT NO. 4 TO CREDIT AGREEMENT

         AMENDMENT dated as of March 14, 2001 to the Amended and Restated Credit
Agreement dated as of September 8, 1999 (as heretofore amended, the "CREDIT
AGREEMENT") among WILLIAMS COMMUNICATIONS, LLC (formerly known as Williams
Communications, Inc., the "BORROWER"), WILLIAMS COMMUNICATIONS GROUP, INC.
("HOLDINGS"), the LENDERS party thereto (the "LENDERS"), BANK OF AMERICA, N.A.,
as Administrative Agent (the "ADMINISTRATIVE AGENT") and THE CHASE MANHATTAN
BANK, as Syndication Agent ("SYNDICATION AGENT").

                                   WITNESSETH:

         WHEREAS, the parties hereto desire to amend the Credit Agreement to,
among other things, (i) increase the maximum permitted amount of aggregate
Incremental Commitments, (ii) provide the Administrative Agent, for the benefit
of the Lenders, with a security interest in certain assets of the Borrower,
Holdings and the Restricted Subsidiaries, as specified in the Credit Agreement
as amended hereby, (iii) update the financial covenants and certain other
covenants, and (iv) revise the margins applicable to fees and the Loans;

         NOW, THEREFORE, the parties hereto agree as follows:

         SECTION 1. Defined Terms; References. Unless otherwise specifically
defined herein, each term used herein which is defined in the Credit Agreement
has the meaning assigned to such term in the Credit Agreement. Each reference to
"hereof", "hereunder", "herein" and "hereby" and each other similar reference
and each reference to "this Agreement" and each other similar reference
contained in the Credit Agreement and each other Loan Document shall, from and
after the Amendment No. 4 Effective Date (as defined in Section 31 below), refer
to the Credit Agreement as amended hereby.

         SECTION 2. Increase in Pricing. (a) The definition of "Applicable
Margin" in Section 1.01 of the Credit Agreement is amended by deleting the chart
set forth therein (the rates per annum set forth in such chart, the "Existing
Margins") and replacing it with the chart set forth below (the rates per annum
set forth in the chart below, the "New Margins"):

<PAGE>   2

<TABLE>
<CAPTION>
                FACILITIES RATING    EURODOLLAR SPREAD       ABR SPREAD        LEVERAGE PREMIUM
                -----------------    -----------------       ----------        ----------------

<S>             <C>                  <C>                     <C>               <C>
LEVEL I         BBB- and Baa3 or           1.50%                0.50%                0.25%
                     higher

LEVEL II           BB+ and Ba1            1.875%               0.875%                0.25%

LEVEL III          BB and Ba2              2.25%                1.25%                0.25%

LEVEL IV           BB- and Ba3             2.50%                1.50%                0.25%

LEVEL V          Lower than BB-
                or lower than Ba3          2.75%                1.75%                0.25%
</TABLE>

         (b) The parties hereto agree that the "Applicable Margin" on any date
prior to the Amendment No. 4 Effective Date shall be determined by reference to
the Existing Margins and on any date on or after the Amendment No. 4 Effective
Date shall be determined by reference to the New Margins.

         SECTION 3. Increase in Letters of Credit Sublimit. Section 2.05(b) of
the Credit Agreement is amended by replacing the amount "$100,000,000" in clause
(i) thereof with the amount "$350,000,000".

         SECTION 4. Increase in Total Amount of Incremental Commitments .
Section 2.20(a) of the Credit Agreement is amended by replacing the amount
"$500,000,000" with the amount "$950,000,000".

         SECTION 5. Exceptions to Mandatory Prepayments and Commitment
Reductions. (a) Clause (a) of the definition of "Prepayment Event" in Section
1.01 of the Credit Agreement is amended by replacing the phrase "clauses (a)
through (d), (f), (g) and (h) of Section 6.05" with the phrase "clauses (a)
through (d) and (f) through (i) of Section 6.05".

         (b) Section 2.08(g) of the Credit Agreement is amended by replacing the
phrase "December 31, 2001" with the phrase "December 31, 2002".

         (c) Section 2.11(c) of the Credit Agreement is amended by replacing the
phrase "December 31, 2001" with the phrase "December 31, 2002".

         SECTION 6. Change in Reporting Requirements. Section 5.01(f) of the
Credit Agreement is amended by inserting the phrase "except to the extent any
such report, proxy statement or other material is available electronically on a
publicly-accessible website" at the end thereof.

         SECTION 7. Sale of Solutions and ATL. (a) The following new definition
is added in alphabetical order in Section 1.01 of the Credit Agreement:

                                       2
<PAGE>   3

                  "ATL" means ATL-Algar Telecom Leste S.A., a Brazilian
         corporation.

         (b) Article 5 of the Credit Agreement is amended by the addition of the
following new Section 5.19 immediately after Section 5.18 thereof:

                           Section 5.19. Sale of Solutions and ATL. (a) Not
                  later than September 30, 2001, Holdings and the Borrower shall
                  have sold, or caused to be sold, to one or more Persons that
                  are not Affiliates of Holdings or any of its Subsidiaries, in
                  one or more transactions (x) all of the capital stock of
                  Solutions held by the Borrower, Holdings or any of its
                  Subsidiaries and/or substantially all of the U.S. and Mexican
                  assets (except aged receivables) of Solutions (and its
                  Subsidiaries) in existence on the Amendment No. 4 Effective
                  Date and (y) all of the capital stock of ATL held by the
                  Borrower, Holdings or any of its Subsidiaries for fair market
                  value and for Net Proceeds in cash in an aggregate amount of
                  at least $700,000,000.

                           (b) Not later than December 31, 2001, Holdings and
                  the Borrower shall have sold or otherwise disposed of, or
                  caused to be sold or otherwise disposed of, to one or more
                  Persons that are not Affiliates of Holdings or any of its
                  Subsidiaries, in one or more transactions, substantially all
                  of the Canadian assets of Solutions (and its Subsidiaries) in
                  existence on the Amendment No. 4 Effective Date.

         SECTION 8. Issuance of Additional Debt or Equity Securities. (a) The
following new definitions are added in alphabetical order in Section 1.01 of the
Credit Agreement:

                           "Incremental Facility Arranger" means each Person
                  acting as a "joint lead arranger" with respect to any
                  Incremental Facility.

                           "Qualifying Issuances" means (i) any issuance of
                  Qualifying Equity Interests of Holdings, (ii) any issuance of
                  unsecured Indebtedness described in clauses (a) or (b) of the
                  definition thereof of Holdings or the Borrower, and (iii) any
                  Sale and Leaseback Transaction by the Borrower or a Restricted
                  Subsidiary the subject property of which is the building under
                  construction as of the Amendment No. 4 Effective Date and
                  adjacent to One Williams Center, together with the parking
                  garage adjacent thereto, or any one or more of three corporate
                  jets identified by the Borrower to the Lenders prior to the
                  Amendment No. 4 Effective Date, so long as the terms and
                  conditions of any such Indebtedness or Sale and Leaseback
                  Transaction shall have been approved by all the

                                       3
<PAGE>   4

                  Incremental Facility Arrangers (if any) and the Administrative
                  Agent prior to the issuance thereof.

         (b) Article 5 of the Credit Agreement is amended by the addition of the
following new Section 5.20 immediately after Section 5.19 thereof:

                           Section 5.20. Qualifying Issuances. Not later than
                  December 31, 2001, the Borrower and/or Holdings shall have
                  consummated Qualifying Issuances for Net Proceeds in cash in
                  an aggregate amount of at least $500,000,000; provided that
                  Net Proceeds in cash in an aggregate amount of not more than
                  $350,000,000 shall have resulted from Qualifying Issuances
                  described in clause (ii) or (iii) of the definition thereof.

         SECTION 9. Additional Permitted Debt. (a) The following new definitions
are added in alphabetical order in Section 1.01 of the Credit Agreement:

                           "Amendment No.4 Effective Date" means the date of
                  effectiveness of Amendment No. 4 to this Agreement.

                           "Structured Note Financing" means the issuance by the
                  Structured Note Trust of notes for cash Net Proceeds of up to
                  $1,500,000,000 substantially on the terms and conditions
                  described by the Borrower in the "Term Sheet for Structured
                  Note" included as an attachment to the Borrower's Amendment
                  Request distributed to the Lenders on or prior to March 7,
                  2001 or otherwise approved by all the Incremental Facility
                  Arrangers (if any) and the Administrative Agent prior to the
                  issuance thereof.

                           "Structured Note Trust" means an Unrestricted
                  Subsidiary created for the purpose of consummating the
                  Structured Note Financing and conducting no activities other
                  than the consummation of the Structured Note Financing and
                  activities incidental thereto.

         (b) Section 6.01 of the Credit Agreement is amended by the insertion of
the following new subsections (r), (s), (t) and (u) immediately after subsection
(q) thereof:

                           (r) Indebtedness of Holdings or the Borrower incurred
                  pursuant to a Qualifying Issuance; provided that the aggregate
                  Net Proceeds in cash received by Holdings and/or the Borrower
                  from the issuance of such Indebtedness, plus the Net Proceeds
                  in cash from any Sale and Leaseback Transaction constituting a
                  Qualifying Issuance shall not exceed $350,000,000;

                                       4
<PAGE>   5

                           (s) Indebtedness with respect to industrial revenue
                  bonds issued for the benefit of the Borrower, Holdings or any
                  Restricted Subsidiary in an aggregate principal or face amount
                  not to exceed $50,000,000;

                           (t) unsecured Indebtedness of Holdings in an
                  aggregate principal amount not to exceed $150,000,000 incurred
                  prior to the consummation of the Structured Note Financing so
                  long as (i) the proceeds of such Indebtedness are used solely
                  to make the capital contributions described in Section 6.04(u)
                  and (ii) the terms and conditions of any such Indebtedness
                  shall have been approved by all the Incremental Facility
                  Arrangers (if any) and the Administrative Agent prior to the
                  issuance thereof;

                           (u) unsecured Indebtedness of Holdings owed to the
                  Structured Note Trust in an aggregate principal amount up to
                  $1,650,000,000 in connection with the consummation of the
                  Structured Note Financing, so long as the terms and conditions
                  of such Indebtedness shall have been approved by all the
                  Incremental Facility Arrangers (if any) and the Administrative
                  Agent prior to the issuance thereof; and

         SECTION 10. Activities of Trading Subsidiary. Section 6.03(c) of the
Credit Agreement is amended by inserting the phrase "a developing or"
immediately prior to the phrase "established market" in clause (v) thereof.

         SECTION 11. Additional Permitted Investments. (a) The definition of
"Additional Capital" in Section 1.01 of the Credit Agreement is amended to read
as follows:

                           "Additional Capital" means the sum of:

                                    (a) $850 million;

                                    (b) the aggregate Net Proceeds received by
                           the Borrower from the issuance or sale of any
                           Qualifying Equity Interests of Holdings, subsequent
                           to the Amendment No. 4 Effective Date; and

                                    (c) the aggregate Net Proceeds from the
                           issuance or sale of Qualifying Holdings Debt
                           subsequent to the Amendment No. 4 Effective Date
                           convertible or exchangeable into Qualifying Equity
                           Interests of Holdings, in each case upon conversion
                           or exchange thereof into

                                       5
<PAGE>   6

                           Qualifying Equity Interests of Holdings subsequent to
                           the Amendment No. 4 Effective Date;

                                    provided, however, that the Net Proceeds
                                    from the issuance or sale of Equity
                                    Interests or Debt described in clause (b) or
                                    (c) shall be excluded from any computation
                                    of Additional Capital to the extent (1)
                                    utilized to make a Restricted Payment or (2)
                                    such Equity Interests or Debt shall have
                                    been issued or sold to the Borrower, a
                                    Subsidiary of the Borrower or a Plan.

         (b) Section 6.04(e) of the Credit Agreement is amended by inserting the
phrase "any Indebtedness of Holdings or the Borrower constituting a Qualifying
Issuance" immediately after the phrase "High Yield Notes" in clause (i) thereof.

         (c) Section 6.04 of the Credit Agreement is amended by (i) deleting the
"and" at the end of subsection (r) thereof and (ii) inserting the following new
subsections (t) and (u) immediately after subsection (s) thereof:

                                    (t) Letters of Credit to support obligations
                           of a Trading Subsidiary incurred in the ordinary
                           course of business; and

                                    (u) capital contributions made by Holdings
                           to the Borrower and by the Borrower to the Structured
                           Note Trust, in each case in an aggregate principal
                           amount not to exceed $150,000,000 and in order to
                           consummate the Structured Note Financing;

         (d) The proviso at the end of Section 6.04 of the Credit Agreement is
amended by deleting all the words contained therein after "shall not exceed" and
replacing them with the following phrase: "the sum of an amount (which amount,
for purposes of this proviso only, shall not be less than zero) equal to (x) the
amount of Additional Capital as of such date minus (y) (A) acquisitions of ADP
Property permitted under Section 6.04(g) made on or prior to such date and (B)
Capital Expenditures permitted under Section 6.08(b) made on or prior to such
date.".

         SECTION 12. Additional Permitted Asset Sales. (a) The definition of
"Permitted Telecommunications Asset Disposition" in Section 1.01 of the Credit
Agreement is amended to read as follows:

                                    "Permitted Telecommunications Asset
                           Disposition" means the transfer, conveyance, sale,
                           lease or other

                                       6
<PAGE>   7

                           disposition of an interest in or capacity on (1)
                           optical fiber and/or conduit and any related
                           equipment, technology or software used in a Segment
                           of the Borrower's and the Restricted Subsidiaries'
                           communications network, other than in the ordinary
                           course of business; provided that after giving effect
                           to such disposition, the Borrower and the Restricted
                           Subsidiaries would retain the right to use at least
                           the minimum retained capacity set forth below:

                           (i) with respect to any Segment constructed by, for
                           or on behalf of the Borrower or any Subsidiary or
                           Affiliate, (x) 24 optical fibers per route mile on
                           such Segment as deployed at the time of such
                           Permitted Telecommunications Asset Disposition or (y)
                           12 optical fibers and one empty conduit per route
                           mile on such Segment as deployed at the time of such
                           Permitted Telecommunications Asset Disposition; and

                           (ii) with respect to any Segment purchased or leased
                           from third parties, the lesser of (x) 50% of the
                           optical fibers per route mile originally purchased or
                           leased on such Segment, (y) 24 optical fibers per
                           route mile on such Segment as deployed at the time of
                           such Permitted Telecommunications Asset Disposition
                           or (z) 12 optical fibers and one empty conduit per
                           route mile on such Segment as deployed at the time of
                           such Permitted Telecommunications Asset Disposition;
                           or

                                    (2) single strand fiber used in a Segment of
                           the Borrower's and the Restricted Subsidiaries'
                           communications network, other than in the ordinary
                           course of business; provided that after giving effect
                           to such disposition, the Borrower and the Restricted
                           Subsidiaries would not eliminate all capacity between
                           the endpoint cities connected by any fiber of the
                           Borrower or its Restricted Subsidiaries.

         (b) Section 6.05 of the Credit Agreement is amended by (i) relettering
existing subsection (h) thereof as clause (j) and amending the cross-reference
in such new subsection (j) and in the proviso at the end of Section 6.05 to
reflect such change and (ii) inserting the following new subsection (h)
immediately after subsection (g) thereof:

                                    (h) the sale, transfer or other dispositions
                           required by Section 5.19;

                                       7
<PAGE>   8

         SECTION 13. Carveout to Sale and Leaseback Transactions Covenant . The
proviso at the end of Section 6.06 of the Credit Agreement is amended to read as
follows: "; provided that the sum of the aggregate amount of Attributable Debt
in respect of all such Sale and Leaseback Transactions permitted under this
clause (ii) at any time outstanding (other than any such Attributable Debt with
respect to any Sale and Leaseback Transaction constituting a Qualifying
Issuance) and the aggregate amount of Indebtedness secured by Liens permitted by
Section 6.02(a)(viii) at such time outstanding shall not exceed 5% of
consolidated net property, plant and equipment of Holdings and the Restricted
Subsidiaries at such time. For purposes of determining compliance with the
proviso set forth in the immediately preceding sentence, Capital Lease
Obligations shall not in any event be included in the calculation of
"Attributable Debt.".

         SECTION 14. Additional Permitted Restricted Payments. (a) The following
new definitions are added in alphabetical order in Section 1.01 of the Credit
Agreement:

                                    "Leverage Target Date" means the first date
                           on or after March 31, 2002 on which the Total
                           Leverage Ratio for the fiscal quarter (or fiscal
                           year, as the case may be) most recently ended and
                           with respect to which Holdings and the Borrower shall
                           have delivered the financial statements required to
                           be delivered by them with respect to such fiscal
                           quarter (or fiscal year, as the case may be) pursuant
                           to Sections 5.01(a) or (b) does not exceed 3.5:1.0.

                                    "Structured Note Bridge Indebtedness" means
                           the Indebtedness permitted to be incurred by Holdings
                           pursuant to Section 6.01(t).

         (b) Section 6.07(a) of the Credit Agreement is amended by (i) deleting
the word "and" immediately preceding clause (iv) and (ii) replacing the period
at the end of such Section 6.07(a) with "; (v) on and after the Leverage Target
Date, Holdings may declare and pay dividends in cash with respect to its
convertible preferred stock outstanding as of the Amendment No. 4 Effective Date
in an amount not exceeding $40,000,000 in any fiscal year and the Borrower may
declare and pay dividends to Holdings to permit Holdings to declare and pay such
dividends and (vi) at any time after the consummation of the Structured Note
Financing, the Borrower may declare and pay a dividend to Holdings so long as
(x) the aggregate amount of such dividend shall not exceed the principal amount
of the Structured Note Bridge Indebtedness outstanding at the time such dividend
is paid plus accrued interest thereon, (y) no Default has occurred and is
continuing or would result therefrom and (z) immediately upon receipt thereof,
Holdings shall

                                       8
<PAGE>   9

apply all of the proceeds of such dividend to repay in full the Structured Note
Bridge Indebtedness then outstanding.

         SECTION 15. Permitted Capital Expenditures. Section 6.08 of the Credit
Agreement is amended to read as follows:

                                    SECTION 6.08. Limitation on Capital
                           Expenditures. (a) Capital Expenditures (other than
                           Capital Expenditures permitted under Section 6.08(b)
                           below) for any fiscal year set forth below shall not
                           exceed the amount set forth below opposite such
                           fiscal year:

<TABLE>
<CAPTION>
FISCAL YEAR                                       AMOUNT
<S>                                           <C>
   2001                                       $2,750,000,000
   2002                                       $2,500,000,000
   2003                                       $2,250,000,000
   2004                                       $2,250,000,000
   2005                                       $2,250,000,000
   2006 and each fiscal year                  $2,800,000,000
   thereafter
</TABLE>

                  provided that if the aggregate amount of Capital Expenditures
                  (other than Capital Expenditures permitted under Section
                  6.08(b) below) actually made in any such period or fiscal year
                  shall be less than the limit with respect thereto set forth
                  above (before giving effect to any increase therein pursuant
                  to this proviso) (the "Base Amount"), then an amount equal to
                  50% of such shortfall may be added to the amount of such
                  Capital Expenditures permitted for the immediately succeeding
                  fiscal year (such amount to be added for any fiscal year, the
                  "Rollover Amount"); provided further that any Capital
                  Expenditures (other than Capital Expenditures permitted under
                  Section 6.08(b) below) made during any fiscal year for which
                  any Rollover Amount shall have been so added shall be applied,
                  first, to the Rollover Amount added for such fiscal year and,
                  second, to the Base Amount for such fiscal year.

         (b) In addition to Capital Expenditures permitted under Section 6.08(a)
above, Holdings and the Restricted Subsidiaries may make (i) Capital
Expenditures consisting of acquisitions of ADP Property permitted under Section
6.04(g) or 6.04(l) and (ii) Capital Expenditures on any date after the Amendment
No.4 Effective Date in an aggregate amount not to exceed Additional Capital as
of such date minus (A) Investments permitted under clause (ii) of the proviso to
Section 6.04 made on or prior to such date and (B) purchases of ADP Property
permitted under Section 6.04(g) made on or prior to such date.

                                       9
<PAGE>   10

         SECTION 16. Total Net Debt to Contributed Capital Covenant. Section
6.15 of the Credit Agreement is amended to read as follows:

                           SECTION 6.15. Total Net Debt to Contributed Capital
                  Ratio. The Total Net Debt to Contributed Capital Ratio shall
                  at no time prior to January 1, 2002 exceed .65 to 1.00.

         SECTION 17. Minimum EBITDA Covenant. Section 6.16 of the Credit
Agreement is amended by deleting the table set forth therein and replacing it
with the following table:

<TABLE>
<CAPTION>
         PERIOD                                                    AMOUNT

<S>                                                                <C>
         January 1, 2001-March 31, 2001                            $200,000,000

         April 1, 2001-June 30, 2001                               $300,000,000

         July 1, 2001-September 30, 2001                           $350,000,000

         October 1, 2001-December 31, 2001                         $350,000,000
</TABLE>

         SECTION 18. Total Leverage Ratio Covenant. Section 6.17(a) of the
Credit Agreement is amended by deleting the table set forth therein and
replacing it with the following table:

<TABLE>
<CAPTION>
                                                                     TOTAL LEVERAGE
         PERIOD                                                           RATIO

<S>                                                                     <C>
         March 31, 2002-December 30, 2002                               12.50:1.00

         December 31, 2002-December 30, 2003                            9.50:1.00

         December 31, 2003 and thereafter                               4.00:1.00
</TABLE>

         SECTION 19. Senior Leverage Ratio Covenant. Section 6.18 of the Credit
Agreement is amended by deleting the table set forth therein and replacing it
with the following table:

<TABLE>
<CAPTION>
                                                                   SENIOR LEVERAGE
         PERIOD                                                         RATIO

<S>                                                                    <C>
         March 31, 2002-December 30, 2002                              5.25:1.00

         December 31, 2002-December 30, 2003                           3.25:1.00

         December 31, 2003 and thereafter                              2.50:1.00
</TABLE>

                                       10
<PAGE>   11

         SECTION 20. Interest Coverage Ratio Covenant. Section 6.19 of the
Credit Agreement is amended by deleting the table set forth therein and
replacing it with the following table:

<TABLE>
<CAPTION>
                                                                  INTEREST COVERAGE
         PERIOD                                                         RATIO

<S>                                                                    <C>
         June 30, 2002-June 29, 2003                                   1.00:1.00

         June 30, 2003-December 30, 2003                               1.50:1.00

         December 31, 2003 and thereafter                              2.00:1.00
</TABLE>

         SECTION 21. Additional Events of Default. Clause (i) of Section 7.01(d)
of the Credit Agreement is amended to read as follows: " (i) Holdings or the
Borrower shall fail to observe or perform any covenant, condition or agreement
contained in Section 5.02, 5.03 (with respect to the existence of Holdings or
the Borrower), 5.10, 5.11A, 5.11B, 5.13, 5.17, 5.18, 5.19 or 5.20 or in Article
6 or".

         SECTION 22. Addition of a Form of Security Agreement. (a) The Credit
Agreement is amended by adding Exhibit K hereto as Exhibit K to the Credit
Agreement.

         SECTION 23. Requirement of Granting of Collateral Upon Borrower Ceasing
to Be a Subsidiary of Parent. (a) The definition of "Collateral Documents" in
Section 1.01 of the Credit Agreement is amended by inserting immediately after
the word "means" the phrase "the Security Agreement and".

         (b) The following new definitions are added in alphabetical order in
Section 1.01 of the Credit Agreement:

                           "Initial Collateral Date" means the first date on
                  which the Parent ceases to own at least a majority of the
                  outstanding securities having ordinary voting power of
                  Holdings, whether as a result of the consummation of the
                  Spin-Off or otherwise.

                           "Security Agreement" means the security agreement
                  substantially in the form of Exhibit K hereto among the
                  Borrower, each Restricted Subsidiary and the Administrative
                  Agent entered into as of the Initial Collateral Date, as
                  amended from time to time.

         (c) Section 5.11 of the Credit Agreement is renumbered Section 5.11B
and a new Section 5.11A is added immediately prior to such new Section 5.11B of
the Credit Agreement, to read in its entirety as follows:

                                       11
<PAGE>   12

                           SECTION 5.11A. Initial Collateral Date. On the
                  Initial Collateral Date, Holdings and the Borrower hereby
                  agree that they will, and will cause each other Restricted
                  Subsidiary to:

                           (a) Deliver to the Administrative Agent duly executed
                  counterparts of the Security Agreement, together with the
                  following:

                                    (i) duly executed counterparts of each
                           supplemental agreement required to be executed and
                           delivered by the terms of the Security Agreement
                           (including, without limitation, any Patent Security
                           Agreement, and Trademark Security Agreement and any
                           Control Agreement, in each case as defined in the
                           Security Agreement);

                                    (ii) stock certificates representing any or
                           all of the outstanding shares of capital stock or
                           other Equity Interests of the Borrower and each
                           Restricted Subsidiary and stock powers and
                           instruments of transfer, endorsed in blank, with
                           respect to such stock certificates;

                                    (iii) any or all documents and instruments,
                           including Uniform Commercial Code financing
                           statements, required by law or reasonably requested
                           by the Administrative Agent to be filed, registered
                           or recorded to create or perfect the Liens intended
                           to be created under the Security Agreement; and

                                    (iv) a completed perfection certificate
                           dated the Initial Collateral Date, in form and
                           substance reasonably satisfactory to the
                           Administrative Agent and signed by an executive
                           officer or Financial Officer of Holdings, together
                           with all attachments contemplated thereby, including
                           the results of a search of the Uniform Commercial
                           Code (or equivalent) filings made with respect to the
                           Loan Parties in the jurisdictions contemplated by
                           such perfection certificate and copies of the
                           financing statements (or similar documents) disclosed
                           by such search and evidence reasonably satisfactory
                           to the Administrative Agent that the Liens indicated
                           by such financing statements (or similar documents)
                           are permitted by Section 6.02 or have been released.

                                       12
<PAGE>   13

                           (b) Deliver to the Administrative Agent a favorable
                  written opinion (addressed to the Agents, the Issuing Banks,
                  the Swingline Lenders and the Lenders and dated the Initial
                  Collateral Date) of each of (i) counsel for Holdings, the
                  Borrower and each Subsidiary Loan Party reasonably acceptable
                  to the Administrative Agent, (ii) the general counsel of
                  Holdings and (iii) local counsel in the jurisdictions where
                  the Borrower is incorporated and where its chief executive
                  office is located and, in the case of each such opinion
                  required by this paragraph, covering such matters relating to
                  the Loan Parties, the Loan Documents, the Collateral and the
                  Transactions as the Administrative Agent (or its counsel) or
                  the Required Lenders shall reasonably request.

         (d) New Section 5.11B(a) of the Credit Agreement is amended by
replacing the initial paragraph thereof with the following:

                           (a) Subject to subsection (d) of this Section 5.11B,
                  deliver to the Administrative Agent duly executed counterparts
                  of the Security Agreement (to the extent not previously
                  delivered pursuant to Section 5.11A) and each other Collateral
                  Document reasonably requested by the Administrative Agent or
                  the Required Lenders, in form and substance satisfactory to
                  the Administrative Agent or the Required Lenders, signed on
                  behalf of Holdings, the Borrower and each Subsidiary Loan
                  Party requested by the Administrative Agent or the Required
                  Lenders, together with (to the extent not previously delivered
                  pursuant to Section 5.11A) such of the following as shall have
                  been so requested:

         (e) New Section 5.11B of the Credit Agreement is amended by adding the
following new subsection (e) immediately after subsection (d) thereof:

                           (e) None of the Borrower, Holdings or any Restricted
                  Subsidiary of Holdings shall be required to grant to the
                  Administrative Agent or any Lender, pursuant to the provisions
                  of this Section 5.11B, a Lien on any of the following assets:
                  (i) voting Equity Interests of any Foreign Subsidiary
                  representing in excess of 66% of the outstanding voting Equity
                  Interests of such Foreign Subsidiary, (ii) any ADP Property to
                  the extent such ADP Property secures any ADP Obligation and
                  (iii) any other asset subject to a security interest permitted
                  by clauses (iv), (v), (viii), or (ix) of Section 6.02 but
                  only, in the case of any asset described in clauses (ii) or
                  (iii), to the extent the granting of such Lien is prohibited
                  by the terms of the agreement pursuant to which such security
                  interest has been granted.

                                       13
<PAGE>   14

         (f) Sections 5.12(a) and (b) of the Credit Agreement are amended in
each case by deleting the phrase "After the occurrence of a Collateral
Establishment Date and for so long as a Collateral Event shall continue
thereafter," at the beginning of each such Section and capitalizing the initial
letter of the following word.

         (g) Section 5.13 of the Credit Agreement is amended as follows:

                           SECTION 5.13. Additional Subsidiaries. (a) If CNG
                  shall become a Subsidiary Loan Party, if Solutions shall
                  determine to become a guarantor under the Subsidiary Guarantee
                  or if any additional Subsidiary is formed or acquired,
                  Holdings and the Borrower will notify the Administrative Agent
                  and the Lenders thereof and if such Subsidiary is a Subsidiary
                  Loan Party, (i) cause such Subsidiary, within ten Business
                  Days after such Subsidiary Loan Party is formed or acquired,
                  to become a party to the Subsidiary Guarantee as an additional
                  guarantor thereunder and to the Security Agreement as a "Lien
                  Grantor" thereunder, (ii) deliver all stock certificates
                  representing the capital stock or other Equity Interests of
                  such Subsidiary to the Administrative Agent, together with
                  stock powers and instruments of transfer, endorsed in blank,
                  with respect to such certificates and (iii) take all actions
                  required under the Security Agreement to perfect, register
                  and/or record the Liens granted by it thereunder and the Lien
                  on such capital stock or other Equity Interests or as may be
                  reasonably requested by the Administrative Agent or the
                  Required Lenders.

                           (b) If a Collateral Establishment Date has occurred
                  and any Collateral Event is then continuing, such Subsidiary
                  is a Subsidiary Loan Party and the Administrative Agent or the
                  Required Lenders so request in writing, Holdings and the
                  Borrower shall (i) within 30 days after such Subsidiary is
                  formed or acquired, cause such Subsidiary to become a party to
                  such Collateral Documents (in addition to the Security
                  Agreement) as the Administrative Agent or the Required Lenders
                  shall request and promptly take such actions as the
                  Administrative Agent or the Required Lenders shall reasonably
                  request to create and perfect Liens on such of such
                  Subsidiary's assets (in accordance with the standards set
                  forth in Section 5.11B(a)) as the Administrative Agent or the
                  Required Lenders shall so request to secure its obligations
                  under the Subsidiary Guarantee, and (ii) within 60 days after
                  such Subsidiary is formed or acquired, cause such Subsidiary
                  to enter into such Mortgage or Mortgages as the Administrative
                  Agent or the Required Lenders shall so request with respect to
                  any or all material

                                       14
<PAGE>   15

                  real property owned by such Subsidiary to secure some or all
                  of its obligations under the Subsidiary Guarantee and to take
                  such actions (including, without limitation, actions of the
                  type referred to in Section 5.11B(a)) with respect thereto as
                  the Administrative Agent or the Required Lenders shall
                  reasonably request.

                           (c) None of the Borrower, Holdings or any Subsidiary
                  Loan Party shall be required to grant to the Administrative
                  Agent or any Lender, pursuant to the provisions of this
                  Section 5.13, a Lien on any of the following assets: (i)
                  voting Equity Interests of any Foreign Subsidiary representing
                  in excess of 66% of the outstanding voting Equity Interests of
                  such Foreign Subsidiary, (ii) any ADP Property to the extent
                  such ADP Property secures any ADP Obligation and (iii) any
                  other asset subject to a security interest permitted by
                  clauses (iv), (v), (viii), or (ix) of Section 6.02 but only,
                  in the case of any asset described in clauses (ii) or (iii),
                  to the extent the granting of such Lien is prohibited by the
                  terms of the agreement pursuant to which such security
                  interest has been granted.

         (h) Section 5.14(a) of the Credit Agreement is amended by (i) deleting
the phrase "After the occurrence of a Collateral Establishment Date and for so
long as a Collateral Event shall continue thereafter," at the beginning there of
and replacing it with the phrase "On any date", (ii) inserting the phrase
"required to be in effect on such date" immediately after the reference to
"Collateral Documents" contained therein and (iii) inserting the phrase
"required to be in effect on such date" at the end of such Section.

         (i) Section 5.14(b) of the Credit Agreement is amended by (i) deleting
the phrase "after any Collateral Establishment Date and prior to the date of a
Collateral Release Event" and (ii) adding the following proviso at the end
thereof: "provided that, none of the Borrower, Holdings or any Subsidiary Loan
Party shall be required to grant to the Administrative Agent or any Lender,
pursuant to the provisions of this Section 5.14, a Lien on any of the following
assets: (i) at any time prior to any Collateral Establishment Date, any assets
of a type other than a type constituting "Collateral" under the form of Security
Agreement set forth on Exhibit K hereto as in effect on the Amendment No. 4
Effective Date, (ii) voting Equity Interests of any Foreign Subsidiary
representing in excess of 66% of the outstanding voting Equity Interests of such
Foreign Subsidiary, (iii) any ADP Property to the extent such ADP Property
secures any ADP Obligation and (iv) any other asset subject to a security
interest permitted by clauses (iv), (v), (viii), or (ix) of Section 6.02 but
only, in the case of any asset described in clauses (iii) or (iv), to the extent
the granting of such Lien is prohibited by the terms of the agreement pursuant
to which such security interest has been granted.

                                       15
<PAGE>   16

         (j) Section 6.02(a)(i) of the Credit Agreement is amended by replacing
the reference to "Section 5.11(d)" with a reference to "Section 5.11B(d)".

         SECTION 24. Permitted Receivables Transactions. (a) The following new
definitions are added in alphabetical order in Section 1.01 of the Credit
Agreement:

                           "Permitted Receivables Disposition" means any
                  transfer (by way of sale, pledge or otherwise) by the Borrower
                  or any Restricted Subsidiary to any other Person (including a
                  Receivables Subsidiary) of accounts receivable and other
                  rights to payment (whether constituting accounts, chattel
                  paper, instruments, general intangibles or otherwise and
                  including the right to payment of interest or finance charges)
                  and related contract and other rights and property (including
                  all general intangibles, collections and other proceeds
                  relating thereto, all security therefor (and the property
                  subject thereto), all guarantees and other agreements or
                  arrangements of whatsoever character from time to time
                  supporting such right to payment, and all other rights, title
                  and interest in goods relating to a sale which gave rise to
                  such right of payment) in connection with a Permitted
                  Receivables Financing.

                           "Permitted Receivables Financing" means any
                  receivables securitization program or other type of accounts
                  receivable financing transaction by the Borrower or any of its
                  Restricted Subsidiaries in an aggregate amount not to exceed
                  $250,000,000 on terms reasonably satisfactory to all the
                  Incremental Facilities Arrangers (if any) and the
                  Administrative Agent.

                           "Receivables Subsidiary" means any wholly-owned
                  Unrestricted Subsidiary (regardless of the form thereof) of
                  the Borrower formed solely for the purpose of, and which
                  engages in no other activities except those necessary for,
                  effecting Permitted Receivables Financings.

         (b) The proviso contained in the definition of "Subsidiary Loan Party"
in Section 1.01 of the Credit Agreement is amended to read in its entirety as
follows "; provided that no Receivables Subsidiary shall be a Subsidiary Loan
Party for any purpose under the Loan Documents.".

         (c) Section 6.01 of the Credit Agreement is amended by inserting the
following new subsection (v) immediately after subsection (u) thereof:

                                       16
<PAGE>   17

                           (v) on any date on or after the Leverage Target Date,
                  Indebtedness of the Borrower owing to a Receivables Subsidiary
                  under a Permitted Receivables Financing;

         (d) Section 6.02(a) of the Credit Agreement is amended by (i) deleting
the "and" at the end of clause (viii) thereof, (ii) inserting an "and" at the
end of clause (ix) thereof and (iii) inserting the following new clause (x)
immediately after clause (ix) thereof:

                           (x) on any date on or after the Leverage Target Date,
                  Liens created in connection with Permitted Receivables
                  Financings, including, without limitation, Liens on proceeds
                  in any form and bank accounts in which any such proceeds are
                  deposited; provided that, except for the assets transferred
                  pursuant to Permitted Receivables Dispositions made in
                  connection with such Permitted Receivables Financings, no such
                  Lien may extend to any assets of Borrower or any Subsidiary of
                  the Borrower that is not a Receivables Subsidiary;

         (e) Section 6.04 of the Credit Agreement is amended by inserting the
following new subsection (v) immediately after subsection (u) thereof:

                           (v) Investments in Receivables Subsidiaries made in
                  connection with Permitted Receivables Financings;

         (f) Section 6.05 of the Credit Agreement is amended by inserting the
following new subsection (i) immediately after subsection (h) thereof:

                           (i) any transfer of Receivables and Related
                  Transferred Rights (each as defined in the Security Agreement
                  attached hereto as Exhibit K) in order to consummate a
                  Permitted Receivables Transaction or to transfer such assets
                  pursuant to a factoring arrangement;

         (g) Section 7.01(g) is amended by inserting the phrase "or Permitted
Receivables Financing" after all three references to "Material Indebtedness"
contained therein.

         SECTION 25. Spin-Off Permitted. (a) The definition of "Change in
Control" in Section 1.01 of the Credit Agreement is amended by (i) inserting
into clause (c) the phrase "other than as a result of the consummation of the
Spin-Off," immediately before the phrase "the failure" contained therein and
(ii) replacing in clause (e) the phrase "other than the Parent" with the phrase
"(other than, prior to the consummation of the Spin-Off, the Parent)".

                                       17
<PAGE>   18

         (b) The following new definition is added in alphabetical order in
Section 1.01 of the Credit Agreement:

                           "Spin-Off" means the distribution by Parent to its
                  shareholders of all or substantially all of the capital stock
                  of Holdings held by Parent substantially on the terms
                  described by the Borrower to the Lenders prior to the
                  Amendment No. 4 Effective Date.

         (c) Section 6.20(a) of the Credit Agreement is amended by adding the
following phrase at the beginning thereof: "At any time prior to the
consummation of the Spin-Off,".

         (d) Section 7.01(p) of the Credit Agreement is amended by adding the
following phrase at the beginning thereof: "at any time prior to the
consummation of the Spin-Off,".

         SECTION 26. Deletion of Provisions Relating to the Intercompany Note .
(a) Section 1.01 of the Credit Agreement is amended by deleting the defined term
"Intercompany Note" contained therein.

         (b) Section 5.10(a) of the Credit Agreement is amended by deleting
clause (iii) thereof and renumbering the subsequent clauses thereof.

         (c) Subsection (l) of Section 6.01 of the Credit Agreement is amended
to read as follows: "(l) [Intentionally deleted];".

         (d) Subsection (n) of Section 6.01 of the Credit Agreement is amended
to read as follows: "(n) [Intentionally deleted];"

         (e) Section 6.02(b) of Credit Agreement is amended by deleting clause
(i) thereof and renumbering the subsequent clauses thereof.

         (f) Section 6.04(g) of the Credit Agreement is amended by deleting
clause (i) thereof and renumbering the subsequent clauses.

         (g) Section 6.07(b) of the Credit Agreement is amended by (x) deleting
the phrase "Intercompany Note," contained therein, (y) replacing in clause (i)
thereof the phrase ", subject, in the case of payments of interest in respect of
the Intercompany Note, to the limitations set forth in Section 6.07(b)(ii) below
and in the Intercreditor Agreements; and " with a period and (z) deleting clause
(ii) thereof in its entirety.

         (h) Section 6.08(b) of the Credit Agreement is amended by replacing the
comma before clause (B) with the word "and" and deleting the phrase "and (C)

                                       18
<PAGE>   19

payments of principal of the Intercompany Note permitted under Section
6.07(b)(ii)(x) made on or prior to such date" contained therein.

         (i) Section 6.10 of the Credit Agreement is amended by deleting the
phrase "Intercompany Note," in clause (i) in the proviso thereto.

         (j) Section 6.13 of the Credit Agreement is amended by deleting clause
(c) thereof and relettering the subsequent clauses.

         (k) Section 6.17 of the Credit Agreement is amended by deleting
subsection (b) thereof.

         SECTION 27. CSI, Inc. No Longer an Unrestricted Subsidiaries. The
definition of "Unrestricted Subsidiaries" contained in Section 1.01 of the
Credit Agreement is amended by deleting the number "(i)" and the entire clause
(ii) thereof, and replacing the word "and" after the phrase "Section 6.14"
contained therein with a period.

         SECTION 28. Representations of Borrower and Holdings. Each of the
Borrower and Holdings represents and warrants that (i) each of the
representations and warranties applicable to it as set forth in Article 3 of the
Credit Agreement will be true on and as of the Amendment No. 4 Effective Date
(except in the case of any such representation or warranty that, by its terms
expressly relates only to a specified earlier date, each of which
representations and warranties was true as of such specified earlier date), and
(ii) no Default will have occurred and be continuing on such date.

         SECTION 29. Governing Law. This Amendment shall be governed by and
construed in accordance with the laws of the State of New York.

         SECTION 30. Counterparts. This Amendment may be signed in any number of
counterparts, each of which shall be an original, with the same effect as if the
signatures thereto and hereto were upon the same instrument.

         SECTION 31. Effectiveness. This Amendment shall become effective on and
as of the date when the following conditions are met (the "AMENDMENT NO. 4
EFFECTIVE DATE"):

                  (a) the Administrative Agent shall have received from each of
         Holdings, the Borrower and the Required Lenders a counterpart hereof
         signed by such party or facsimile or other written confirmation (in
         form satisfactory to the Administrative Agent) that such party has
         signed a counterpart hereof;

                                       19
<PAGE>   20

                  (b) the Administrative Agent shall have received from each
         Subsidiary Loan Party an acknowledgment in form and substance
         reasonably satisfactory to the Administrative Agent to the effect that
         the obligations of the Borrower and Holdings under the Credit Agreement
         as amended hereby constitute "Guaranteed Obligations" of such
         Subsidiary Loan Party under the Subsidiary Guarantee;

                  (c) the Administrative Agent shall have received such
         documents and certificates as the Administrative Agent or its counsel
         may reasonably request relating to the organization, existence and good
         standing of each Loan Party, the authorization of the transactions
         contemplated hereby and any other legal matters relating to the Loan
         Parties, the Loan Documents or the transactions contemplated hereby,
         all in form and substance satisfactory to the Administrative Agent and
         its counsel;

                  (d) the Administrative Agent shall have received a
         certificate, dated the Amendment No. 4 Effective Date and signed by the
         President, a Vice President or a Financial Officer of the Borrower,
         confirming compliance with the matters set forth in Section 28 of this
         Amendment;

                  (e) the Administrative Agent shall have received evidence
         satisfactory to it that the Intercreditor Agreement with respect to the
         ADP shall be in full force and effect on the terms in effect
         immediately prior to the effectiveness of this Amendment;

                  (f) the Administrative Agent shall have received all fees and
         other amounts due and payable on or prior to the Amendment No. 4
         Effective Date, including, to the extent invoiced, reimbursement or
         payment of all out-of-pocket expenses required to be reimbursed or paid
         by any Loan Party hereunder or under any other Loan Document;

                  (g) the Lenders shall have received, and shall be satisfied
         with, (i) audited consolidated financial statements of Holdings for the
         fiscal years ended December 31, 1999 and December 31, 2000 (if
         available) and (ii) satisfactory unaudited interim consolidated
         financial statements of the Borrower and Holdings for each fiscal
         quarterly period ended subsequent to the date of the latest financial
         statements delivered pursuant to clause (i) of this paragraph as to
         which such financial statements are available;

                  (h) the Lenders shall have received, and shall be satisfied
         with, Holdings and the Borrower's projected annual pro forma balance

                                       20
<PAGE>   21

         sheets, statements of operations and cash flows for the fiscal years
         2001 through 2007, in each of the foregoing cases (i) after giving
         effect to Borrowings under the Incremental Facilities (in the maximum
         aggregate amount permitted under the Credit Agreement as amended by
         this Amendment) and the Structured Note Financing (as defined in the
         Credit Agreement as amended by this Amendment) and (ii) after giving
         effect to the transactions described in clause (i) and, in addition,
         the sale of all of the capital stock or all or substantially all of the
         assets of Solutions;

                  (i) there shall be no actions, suits or proceedings by or
         before any arbitrator or Governmental Authority pending against or, to
         the knowledge of Holdings or the Borrower, threatened against or
         affecting Holdings or any Subsidiary (i) as to which there is a
         reasonable possibility of an adverse determination and that, if
         adversely determined, could reasonably be expected, individually or in
         the aggregate, to result in a Material Adverse Effect (other than the
         Disclosed Matters) or (ii) that involve any of the Loan Documents or
         the transactions contemplated by this Amendment;

                  (j) since December 31, 1999, there shall have been no Material
         Adverse Change;

                  (k) the Administrative Agent shall have received evidence
         reasonably satisfactory to it that the Borrower shall have entered into
         one or more hedging transactions with respect to the portfolio of
         equity securities investments referred to by the Borrower as the "Tech
         Farm investments" on terms and conditions reasonably satisfactory to
         the Administrative Agent; and

                  (l) the Administrative Agent shall have received a solvency
         certificate, in form and substance reasonably satisfactory to the
         Administrative Agent, from the Financial Officer of each of Holdings
         and the Borrower.

                                       21
<PAGE>   22

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

                                       WILLIAMS COMMUNICATIONS, LLC

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

                                       WILLIAMS COMMUNICATIONS GROUP, INC.

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

                                       BANK OF AMERICA, N.A.

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

                                       THE CHASE MANHATTAN BANK

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

                                       [OTHER LENDERS]

                                       22
<PAGE>   23

                                                                       EXHIBIT K

                           FORM OF SECURITY AGREEMENT

                                    [to come]

                                       23

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