Document:

<PAGE>

                                                                   EXHIBIT 10.25

        AMENDMENT NO. 3 TO AMENDED AND RESTATED CREDIT AGREEMENT AMONG
    IPC INFORMATION SYSTEMS, INC., AS PARENT BORROWER, IPC FUNDING CORP.,
       AS SUB BORROWER, IPC COMMUNICATIONS, INC., AS A LOAN PARTY, THE
       LENDERS SIGNATORY THERETO, AS LENDERS, GENERAL ELECTRIC CAPITAL
        CORPORATION, AS ISSUING BANK, COLLATERAL AGENT, ADMINISTRATIVE
         AGENT AND LENDER, AND FIRST UNION CAPITAL MARKETS, INC., AS
                              DOCUMENTATION AGENT

          This Amendment No. 3 to Amended and Restated Credit Agreement, dated
as of September 24, 1999 (this "Amendment"), is entered into by and among IPC
Information Systems, Inc., a Delaware corporation (the "Parent Borrower"); IPC
Funding Corp., a Delaware corporation (the "Sub Borrower"); IPC Communications,
Inc., a Delaware corporation ("Holdings"), as a Loan Party; General Electric
Capital Corporation, as a Lender, and as Collateral Agent, Issuing Bank and
Administrative Agent (the "Administrative Agent") for the Lender Parties; and
the other Lenders.

                                   RECITALS

          A.  Borrowers, Holdings, the Administrative Agent, the Lenders and
First Union Capital Markets, Inc., as Documentation Agent, are parties to that
certain Amended and Restated Credit Agreement, dated as of June 21, 1999 (as
amended by Amendment No. 1 thereto, dated as of July 1, 1999, and Amendment No.
2 thereto, dated as of August 12, 1999, the "Credit Agreement").

          B.  Borrowers, Holdings, the Administrative Agent and the Lenders are
desirous of amending certain sections of, and waiving certain requirements
under, the Credit Agreement, as and to the extent set forth in this Amendment.

              NOW THEREFORE, in consideration of the premises and the mutual
covenants hereinafter contained, and of the loans or other extensions of credit
heretofore, now or hereafter made to, or for the benefit of, Borrowers by
Lenders, Borrowers, Holdings, the Administrative Agent and Lenders hereby agree
as follows:

          1.  Definitions.  Except to the extent otherwise specified herein,
              -----------
capitalized terms used in this Amendment shall have the same meanings ascribed
to them in the Credit Agreement.

          2.  Amendment.
              ---------

              2.1.  Section 1.01 of the Credit Agreement is hereby amended by
inserting the following definitions in the proper alphabetical order:

              "TIBCO' means TIBCO Finance Technology Inc., a Delaware
               -----
              corporation."

              "TIBCO Agreements' means (a) the TIBCO Strategic Agreement, (b)
               ----------------
              that certain License, Development, Embedding, Support & Royalty
              Agreement, dated as June 25, 1999, by and between TIBCO and IXnet,
              as amended by Addendum One dated June 30, 1999, Addendum Two dated
              July 30, 1999 and Addendum Three dated August 31, 1999, and as to
              be further amended by Addendum Four dated
<PAGE>

          September 24, 1999 and Addendum Five dated September 24, 1999, and (c)
          that certain Network and Services and Joint Solutions Agreement, dated
          as of September 24, 1999 by and between TIBCO and IXnet."

          " TIBCO Strategic Agreement' means that certain Strategic Agreement,
            -------------------------
          dated as of September 24, 1999, by and among TIBCO, IXnet Holdings and
          IXnet."

          2.2.  Section 1.01 of the Credit Agreement is hereby further amended
by deleting the definition of "Capital Expenditures" in its entirety and
replacing it with the following:

          " Capital Expenditures' means, for any Person for any period, all
            --------------------
          expenditures (by the expenditure of cash or the incurrence of Debt,
          including Obligations under Capitalized Leases) by such Person for the
          purchase or other acquisition of any fixed, capital or other assets or
          improvements or for replacements, substitutions or additions thereto,
          that have a useful life of more than one year and that are required to
          be capitalized under GAAP."

          2.3.  Section 5.02(b) of the Credit Agreement is hereby amended by
deleting the word "and" from the end of clause (ii)(A) thereof, by inserting the
word "and" at the end of clause (ii)(B) thereof and inserting the following as a
new clause (ii)(C):

          "(C) in the case of IXnet, unsecured Debt consisting of (1) the
     deferred purchase price owed to TIBCO in an amount not to exceed
     $10,000,000 in connection with the acquisition by IXnet of certain
     perpetual product licenses and other services and license rights from TIBCO
     pursuant to the TIBCO Agreements and (2) deferred payments in respect of
     indefeasible rights of use ("IRU's") in an aggregate amount not to exceed
     $16,500,000; provided, that, (w) in the case of Debt under clause (1)
                  --------  ----
     above, such Debt shall be on the terms set forth in the TIBCO Strategic
     Agreement (as in effect on the date hereof) and such other terms and
     conditions as shall be satisfactory to the Administrative Agent, (x) in the
     case of Debt under clause (2) above, such Debt shall be on customary terms
     for IRU's and otherwise satisfactory to the Administrative Agent, (y) an
     amount of cash equal to the entire amount of the Debt permitted under this
     clause (C) that is outstanding at any time shall be placed in a blocked
     bank account under the control of the Administrative Agent and pledged to
     the Administrative Agent for the ratable benefit of the Administrative
     Agent and the other Secured Parties on terms and conditions satisfactory to
     the Administrative Agent and (z) the Administrative Agent shall have
     received evidence satisfactory to the Administrative Agent that a valid and
     perfected first priority security interest in the licenses, intellectual
     property and other rights that IXnet has acquired pursuant to the TIBCO
     Agreements and under each of the IRU's has been granted to the
     Administrative Agent for the ratable benefit of the Administrative Agent
     and the other Secured Parties and that all actions necessary or desirable
     in connection therewith, including, by way of example but not of
     limitation, all necessary or desirable written notices from IXnet to TIBCO
     in respect of the TIBCO Agreements, have been taken,"

                                       2
<PAGE>

         2.4.  Section 5.02(g) of the Credit Agreement is hereby amended by
deleting from the twelfth line thereof the word "and" that appears after the
number "(ii)" and before the number "(iii)" and replacing it with a comma (i.e.
a ","), by inserting after the number "(iii)" and before the word "below" in
such twelfth line the words "and (iv)", and by inserting after the words
"Administrative Agent" and before the period at the end of such Section 5.02(g),
the following:

         "and (iv) IXnet Holdings may issue up to 500,000 shares of its common
     stock to TIBCO as set forth in the TIBCO Strategic Agreement (as in effect
     on the date hereof); provided, that, such 500,000 shares do not exceed at
                          --------  ----
     the time of issuance one percent (1%) of the common stock of IXnet Holdings
     on a fully diluted basis; provided, further, that, the sum of such 500,000
                               --------  -------  ----
     shares and the shares of IXnet Holdings issued pursuant to clause (iii)(C)
     of this Section 5.02(g) does not at any time exceed twenty percent (20%) of
     the common stock of IXnet Holdings"

         2.5.  Section 5.04(c) of the Credit Agreement is hereby amended by
inserting after the word "below" and before the colon in the fourth line thereof
the following:

         "(provided, however, that, solely for the periods ending on September
           --------  -------  ----
     30, 1999, December 31, 1999, March 31, 2000 and June 30, 2000, any amount
     of Debt expressly permitted under Section 5.02(b)(ii)(C) (including,
     without limitation, clause (y) thereof) that is outstanding at such time
     shall not be included in the calculation of the Leverage Ratio for such
     period)"

          2.6.  Section 5.04(d) of the Credit Agreement is hereby amended by
inserting after the word "period" and before the colon in the twenty-third line
thereof the following:

         "(provided, however, that, solely for the periods ending on September
           --------  -------  ----
     30, 1999, December 31, 1999, March 31, 2000 and June 30, 2000, any amount
     of Debt expressly permitted under Section 5.02(b)(ii)(C) (including,
     without limitation, clause (y) thereof) that is outstanding at such time
     shall not be included in the calculation of the Fixed Charge Coverage Ratio
     for such period)"

     3.  Waiver.  The Agents and Lenders hereby extend the requirements of
         ------
Section 5.03(d) for the Fiscal Year ending September 30, 1999 from September 15,
1999 until October 30, 1999 (the "Waiver Termination Date").  On the Waiver
Termination Date, without any further action by the Administrative Agent, the
Lender Parties or any other Person, all of the terms and provisions set forth in
Section 5.03(d) of the Credit Agreement that are waived under this Section 3 of
this Amendment shall automatically apply and have the same force and effect as
if Section 3 of this Amendment had not been entered into by the parties hereto
and did not exist, and the Administrative Agent and the Lender Parties shall
have all of the rights and remedies afforded to them under the Credit Agreement
and the other Loan Documents as though no waiver had been granted by them under
this Section 3.

     4.  TIBCO Blocked Account Procedures.  The Administrative Agent, the
         --------------------------------
Parent Borrower and IXnet hereby agree as follows with respect to the blocked
account (the "TIBCO

                                       3
<PAGE>

Blocked Account") required by clause (y) of Section 5.02(b)(ii)(C) of the Credit
Agreement as amended by this Amendment:

          4.1.  The Parent Borrower and IXnet agree to deposit into the TIBCO
Blocked Account such amounts in cash such that the balance in the TIBCO Blocked
Account shall at all times be at least equal to the entire amount of Debt
permitted under Section 5.02(b)(ii)(C) of the Credit Agreement that is
outstanding at such time;

          4.2.  The Administrative Agent agrees to permit IXnet to make
withdrawals from the TIBCO Blocked Account in such amounts and at such times as
shall be necessary for the sole purpose of (1) making scheduled payments to
TIBCO pursuant to Section 2 of the TIBCO Strategic Agreement and (2) making
scheduled payments in respect of the IRU's;

          4.3.  The TIBCO Blocked Account shall be kept at First Union National
Bank and shall be subject to and governed by a blocked account agreement (the
"TIBCO Blocked Account Agreement") in favor of the Administrative Agent, on
 -------------------------------
behalf of the Administrative Agent and the other Secured Parties, which
agreement shall be in form and substance satisfactory to the Administrative
Agent.

     5.   Acknowledgment and Consent of Guarantors.  Each Guarantor hereby
          ----------------------------------------
consents to this Amendment and hereby confirms and agrees that (a)
notwithstanding the effectiveness of this Amendment or any of the other prior
amendments comprising part of the Credit Agreement, the Guaranty and each other
Loan Document to which it is a party is, and shall continue to be, in full force
and effect and is hereby ratified and confirmed in all respects, and (b) the
Collateral Documents to which such Guarantor is a party and all of the
Collateral described therein do, and shall continue to, secure the payment of
all of the Secured Obligations (in each case, as defined therein).

     6.   Conditions Precedent to Amendment.  The Amendment shall be effective
          ---------------------------------
upon satisfaction of each of the following conditions precedent:

          6.1.  This Amendment shall have been duly executed and delivered by
each of Borrowers, Holdings, the Guarantors, IXnet (as to Section 4 hereof), the
Administrative Agent and Required Lenders.

          6.2.  The TIBCO Blocked Account Agreement shall have been duly
executed and delivered by each of the parties thereto and the TIBCO Blocked
Account shall have been funded as required by Section 4 of this Amendment.

          6.3.  IXnet shall have given notice to TIBCO that IXnet has granted a
security interest in the licenses, intellectual property and other rights that
IXnet has acquired from TIBCO pursuant to the TIBCO Agreements to the
Administrative Agent for the ratable benefit of the Administrative Agent and the
other Secured Parties.

                                       4
<PAGE>

     7.   Reference to and Effect Upon the Credit Agreement and other Loan
          ----------------------------------------------------------------
Agreements.
----------

          7.1.  Except as specifically amended in Section 2 above or waived in
Section 3 above, the Credit Agreement, the Notes and each other Loan Document
shall remain in full force and effect and each is hereby ratified and confirmed.

          7.2.  The execution, delivery and effect of this Amendment shall be
limited precisely as written and shall not be deemed to (i) be a consent to any
waiver of any term or condition (except as specifically waived in Section 3
above), or to any amendment or modification of any term or condition (except as
specifically amended in Section 2 above), of the Credit Agreement or any other
Loan Document or (ii) prejudice any right, power or remedy which any Agent or
any Lender now has or may have in the future under or in connection with the
Credit Agreement, the Notes or any other Loan Document.  Each reference in the
Credit Agreement to "this Agreement", "hereunder", "hereof", "herein" or any
other word or words of similar import shall mean and be a reference to the
Credit Agreement as amended hereby, and each reference in any other Loan
Document to the Credit Agreement or any word or words of similar import shall be
and mean a reference to the Credit Agreement as amended hereby.

     8.   Counterparts.  This Amendment may be executed in any number of
          ------------
counterparts, each of which when so executed shall be deemed an original but all
such counterparts shall constitute one and the same instrument.  Delivery of an
executed counterpart by facsimile shall be as effective as delivery of a
manually signed original counterpart.

     9.   Costs and Expenses.  As provided in Section 8.04 of the Credit
          ------------------
Agreement, Borrowers shall pay the fees, costs and expenses incurred by the
Administrative Agent in connection with the preparation, execution and delivery
of this Amendment (including, without limitation, attorneys' fees).

     10.  GOVERNING LAW.  THIS AMENDMENT SHALL BE GOVERNED BY AND CONSTRUED
          -------------
IN ACCORDANCE WITH THE INTERNAL LAWS (AS OPPOSED TO CONFLICTS OF LAW PROVISIONS)
OF THE STATE OF NEW YORK.

     11.  Headings.  Section headings in this Amendment are included herein
          --------
for convenience of reference only and shall not constitute a part of this
Amendment for any other purpose.

                           [Signature Pages Follow]

                                       5
<PAGE>

          IN WITNESS WHEREOF, this Amendment No. 3 to Amended and Restated
Credit Agreement has been duly executed as of the date first written above.

                              IPC INFORMATION SYSTEMS, INC.,
                              as Parent Borrower

                              By: _________________________

                              Title:_______________________

                              IPC FUNDING CORP.,
                              as Sub Borrower

                              By:__________________________

                              Title:_______________________

                              IPC COMMUNICATIONS, INC.,
                              as a Loan Party

                              By:__________________________

                              Title:______________________

                              GENERAL ELECTRIC CAPITAL CORPORATION,
                              as Administrative Agent, Collateral Agent, Issuing
                              Bank and Lender

                              By:__________________________

                              Title:_______________________

                              FIRST UNION NATIONAL BANK,
                              as a Lender

                              By: ___________________________

                              Title: ________________________

                              GMAC COMMERCIAL CREDIT LLC,
                              as a Lender

                              By: _________________________

                              Title:_______________________

                              INTERNATIONAL EXCHANGE NETWORKS,
                              LTD., as a Guarantor and as to Section 4 hereof

                              By: _________________________

                              Title:_______________________
<PAGE>

                              INTERNATIONAL EXCHANGE NETWORK CORP.,
                              as a Guarantor

                              By: _________________________

                              Title:_______________________

                              HNG CORP., as a Guarantor

                              By: _________________________

                              Title:_______________________

                              IPC MERGER SUB, INC., as a Guarantor

                              By: _________________________

                              Title:_______________________

                              IXNET, INC., as a Guarantor

                              By: _________________________

                              Title:_______________________

                              IPC INFORMATION SYSTEMS FAR EAST INC., as
                              a Guarantor

                              By: _________________________

                              Title:_______________________

                              MXNET INC., as a Guarantor

                              By: _________________________

                              Title:_______________________

                              IPC INFORMATION SYSTEMS ASIA
                              PACIFIC, LIMITED, as a Guarantor

                              By: _________________________

                              Title:_______________________

<PAGE>

                              IPC INFORMATION SYSTEMS CANADA, INC., as
                              a Guarantor

                              By: _________________________

                              Title:_______________________

                              IXNET UK LIMITED, as a Guarantor

                              By: _________________________

                              Title:_______________________

                              IPC INFORMATION SYSTEMS, as a Guarantor

                              By: _________________________

                              Title:_______________________

                              IPC UK HOLDINGS, LTD., as a Guarantor

                              By: _________________________

                              Title:_______________________

                              IPC UK SPC LIMITED, as a Guarantor

                              By: _________________________

                              Title:_______________________

                              SATURN GLOBAL NETWORK SERVICES
                              HOLDINGS LIMITED, as a Guarantor

                              By: _________________________

                              Title:_______________________

                              IXNET AUSTRALIA PTY LIMITED, as a Guarantor

                              By: _________________________

                              Title:_______________________
<PAGE>

                              SATURN GLOBAL NETWORK SERVICES (HONG
                              KONG) LIMITED, as a Guarantor

                              By: _________________________

                              Title:_______________________

                              SATURN GLOBAL NETWORK SERVICES
                              (JAPAN) LTD., as a Guarantor

                              By: _________________________

                              Title:_______________________

                              SATURN GLOBAL NETWORK SERVICES
                              (SINGAPORE) PTE LTD., as a Guarantor

                              By: _________________________

                              Title:_______________________<PAGE>

                                                                   EXHIBIT 10.26

AMENDMENT NO. 4 TO AMENDED AND RESTATED CREDIT AGREEMENT AMONG IPC INFORMATION
  SYSTEMS, INC., AS PARENT BORROWER, IPC FUNDING CORP., AS SUB BORROWER, IPC
   COMMUNICATIONS, INC., AS A LOAN PARTY, THE LENDERS SIGNATORY THERETO, AS
  LENDERS, GENERAL ELECTRIC CAPITAL CORPORATION, AS ISSUING BANK, COLLATERAL
AGENT, ADMINISTRATIVE AGENT AND LENDER, AND FIRST UNION CAPITAL MARKETS, INC.,
                            AS DOCUMENTATION AGENT

          This Amendment No. 4 to Amended and Restated Credit Agreement, dated
as of December 1, 1999 and effective as of September 30, 1999 (this
"Amendment"), is entered into by and among IPC Information Systems, Inc., a
Delaware corporation (the "Parent Borrower"); IPC Funding Corp., a Delaware
corporation (the "Sub Borrower"); IPC Communications, Inc., a Delaware
corporation ("Holdings"), as a Loan Party; General Electric Capital Corporation,
as a Lender, and as Collateral Agent, Issuing Bank and Administrative Agent (the
"Administrative Agent") for the Lender Parties; and the other Lenders.

                                   RECITALS

          A.  Borrowers, Holdings, the Administrative Agent, the Lenders and
First Union Capital Markets, Inc., as Documentation Agent, are parties to that
certain Amended and Restated Credit Agreement, dated as of June 21, 1999 (as
amended by Amendment No. 1 thereto, dated as of July 1, 1999, Amendment No. 2
thereto, dated as of August 12, 1999, and Amendment No.3 thereto, dated as of
September 24, 1999, the "Credit Agreement").

          B.  Borrowers, Holdings, the Administrative Agent and the Lenders are
desirous of amending certain sections of, and making certain other changes to
the Credit Agreement, as and to the extent set forth in this Amendment and
subject to the terms and conditions set forth herein.

          NOW THEREFORE, in consideration of the premises and the mutual
covenants hereinafter contained, and of the loans or other extensions of credit
heretofore, now or hereafter made to, or for the benefit of, Borrowers by
Lenders, Borrowers, Holdings, the Administrative Agent and Lenders hereby agree
as follows:

1.   Definitions.  Except to the extent otherwise specified herein, capitalized
     -----------
terms used in this Amendment shall have the same meanings ascribed to them in
the Credit Agreement.

2.   Amendments and Covenants.
     ------------------------

     2.1. Section 5.04(c) of the Credit Agreement is hereby amended by deleting
the ratio "6.60:1.00" that appears opposite the date "September 30, 1999" and
replacing it with the ratio "7.70 :1.00".

     2.2. Section 5.04(d) of the Credit Agreement is hereby amended by deleting
the ratio "1.28:1.00" that appears opposite the date "September 30, 1999" and
replacing it with the ratio "1.07 :1.00".
<PAGE>

     2.3  The Parent Borrower shall maintain as at the end of October 31,1999,
EBITDA of not less than $36,000,000 for the trailing twelve month period then
ended.

     2.4  The Parent Borrower shall maintain as at the end of October 31, 1999 a
ratio of Consolidated EBITDA to cash interest payable on all Debt of the Parent
Borrower and its Subsidiaries, for the trailing twelve month period ending
October 31, 1999, of not less than 4.00:1.00.

     2.5  The Parent Borrower shall maintain as at the end of October 31, 1999 a
Leverage Ratio of  the Parent Borrower and its Subsidiaries, for the trailing
twelve month period ending October 31, 1999, of not more than 6.60:1.00.

     2.6  The Parent Borrower shall maintain as at the end of October 31, 1999 a
ratio of (i) EBITDA for the trailing twelve month period of the Parent Borrower
and its Subsidiaries, less Capital Expenditures made by the Parent Borrower and
                      ----
its Subsidiaries during such period, other than (x) Capital Expenditures to the
extent financed by Capitalized Leases (but only to the extent so financed and
not paid in cash), (y) Capital Expenditures to the extent financed by purchase
money indebtedness (but only to the extent so financed and not paid in cash) and
(z) Capital Expenditures made by IXnet and its Subsidiaries out of the IPO Net
Cash Proceeds (but only to the extent so made out of the IPO Net Cash Proceeds)
(in the case of (x), (y) and (z) only to the extent that such transactions are
permitted by, and its compliance with, the terms and conditions of this
Agreement), less the aggregate amount of federal, state, local and foreign
            ----
income taxes paid by the Parent Borrower and its Subsidiaries in cash during
such period, other than (x) various foreign income taxes paid by Foreign
Subsidiaries to the extent that such foreign income taxes do not in the
aggregate exceed $1,000,000 during such period, (y) the payment by IPC UK in
June 1999 of certain foreign income taxes in the aggregate amount of
approximately (Pounds)4,200,000 and (z) the payment by IPC UK in July 1999 of
the ACT (Advance Corporation Tax) in the aggregate amount of approximately
(Pounds)5,625,000, less cash dividends paid by the Parent Borrower to the holder
                   ----
of its common stock (i.e. Holdings) during such period to the extent that the
Parent Borrower is expressly permitted to pay such dividends under this
Agreement, to the (ii) sum of (x) cash interest payable by the Parent Borrower
and its Subsidiaries on all Debt during such period plus (y) principal amounts
                                                    ----
of all Debt payable by the Parent Borrower and its Subsidiaries during such
twelve month period ending October 31, 1999, of not less than 1.28:1.00 for such
period ending October 31, 1999.

     2.7  The Parent Borrower shall furnish to the Lender Parties and the Agents
no later than December 15, 1999, monthly financial statements as at and for the
twelve month period ended October 31, 1999, including balance sheets, statements
of income and statements of cash flows, which shall be prepared in a manner
consistent with the quarterly financial statements required under Section 5.03
of the Credit Agreement, shall be certified by the chief financial officer of
Holdings and the Parent Borrower in a manner consistent with the certification
of the quarterly financial  statements required under Section 5.03, shall
demonstrate compliance with each of the financial covenants set forth in
Sections 2.3 through 2.5, inclusive, of this Amendment and shall otherwise be in
form and substance acceptable to the Administrative Agent and Lenders.

                                       2
<PAGE>

     2.8  The failure to perform or observe any of the covenants or agreements
contained in Sections 2.3 through 2.6, inclusive, of this Amendment shall
constitute an immediate "Event of Default" under the Credit Agreement, as and to
the same extent as if such failure to perform or observe any of such covenants
or agreements was an "Event of Default" under Section 6.01 (c) of the Credit
Agreement.

3.   Acknowledgment and Consent of Guarantors.  Each Guarantor hereby consents
     ----------------------------------------
to this Amendment and hereby confirms and agrees that (a) notwithstanding the
effectiveness of this Amendment or any of the other prior amendments comprising
part of the Credit Agreement, the Guaranty and each other Loan Document to which
it is a party is, and shall continue to be, in full force and effect and is
hereby ratified and confirmed in all respects, and (b) the Collateral Documents
to which such Guarantor is a party and all of the Collateral described therein
do, and shall continue to, secure the payment of all of the Secured Obligations
(in each case, as defined therein).

4.   Conditions Precedent to Amendment.  This Amendment shall be effective upon
     ---------------------------------
satisfaction of each of the following conditions precedent:

     4.1. This Amendment shall have been duly executed and delivered by each of
the Borrowers, Holdings, the Guarantors, the Administrative Agent and Required
Lenders.

     4.2. The Parent Borrower shall have paid an amendment fee in an amount
equal to $65,000 to the Administrative Agent, for the pro rata account of each
Lender that timely executes and delivers its signature page evidencing its
agreement to this Amendment.

     4.3. All of the representations and warranties contained in the Credit
Agreement and any other documents executed in connection therewith are true and
correct on and as of the date hereof as though made on the date hereof.

5.   Reference to and Effect Upon the Credit Agreement and other Loan
     ----------------------------------------------------------------
Agreements.
-----------

     5.1. Except as specifically amended in Section 2, the Credit Agreement, the
Notes and each other Loan Document shall remain in full force and effect and
each is hereby ratified and confirmed.

     5.2. The execution, delivery and effect of this Amendment shall be limited
precisely as written and shall not be deemed to (i) be a consent to any waiver
of any term or condition, or to any amendment or modification of any term or
condition (except as specifically amended in Section 2), of the Credit Agreement
or any other Loan Document or (ii) prejudice any right, power or remedy which
any Agent or any Lender now has or may have in the future under or in connection
with the Credit Agreement, the Notes or any other Loan Document.  Each reference
in the Credit Agreement to "this Agreement", "hereunder", "hereof", "herein" or
any other word or words of similar import shall mean and be a reference to the
Credit Agreement as amended hereby, and each reference in any other Loan
Document to the Credit Agreement or any word or words of similar import shall be
and mean a reference to the Credit Agreement as amended hereby.

                                       3
<PAGE>

6.   Counterparts.  This Amendment may be executed in any number of
     ------------
counterparts, each of which when so executed shall be deemed an original but all
such counterparts shall constitute one and the same instrument.  Delivery of an
executed counterpart by facsimile shall be as effective as delivery of a
manually signed original counterpart.

7.   Costs and Expenses.  As provided in Section 8.04 of the Credit Agreement,
     ------------------
Borrowers shall pay the fees, costs and expenses incurred by the Administrative
Agent in connection with the preparation, execution and delivery of this
Amendment (including, without limitation, attorneys' fees).

8.   GOVERNING LAW.  THIS AMENDMENT SHALL BE GOVERNED BY AND CONSTRUED IN
     -------------
ACCORDANCE WITH THE INTERNAL LAWS (AS OPPOSED TO CONFLICTS OF LAW PROVISIONS) OF
THE STATE OF NEW YORK.

9.   Headings.  Section headings in this Amendment are included herein for
     --------
convenience of reference only and shall not constitute a part of this Amendment
for any other purpose.

                           [Signature Pages Follow]

                                       4
<PAGE>

          IN WITNESS WHEREOF, this Amendment No. 4 to Amended and Restated
Credit Agreement has been duly executed as of the date first written above.

                               IPC INFORMATION SYSTEMS, INC.,
                               as Parent Borrower

                               By: _________________________

                               Title:_______________________

                               IPC FUNDING CORP.,
                               as Sub Borrower

                               By:__________________________

                               Title:_______________________

                               IPC COMMUNICATIONS, INC.,
                               as a Loan Party

                               By:__________________________

                               Title:_______________________

                               GENERAL ELECTRIC CAPITAL CORPORATION,
                               as Administrative Agent, Collateral Agent,
                               Issuing Bank and Lender

                               By:__________________________

                               Title:_______________________

                               FIRST UNION NATIONAL BANK,
                               as a Lender

                               By: _________________________

                               Title: ______________________

                               GMAC COMMERCIAL CREDIT LLC,
                               as a Lender

                               By: _________________________

                               Title:_______________________

                               INTERNATIONAL EXCHANGE NETWORKS, LTD., as a
                               Guarantor

                               By: _________________________

                               Title:_______________________

<PAGE>

                               INTERNATIONAL EXCHANGE NETWORK CORP., as a
                               Guarantor

                               By: _________________________

                               Title:________________________

                               HNG CORP., as a Guarantor

                               By: _________________________

                               Title:________________________

                               V BAND CORPORATION, as a Guarantor

                               By: _________________________

                               Title:________________________

                               IXNET, INC., as a Guarantor

                               By: _________________________

                               Title:________________________

                               IPC INFORMATION SYSTEMS FAR EAST INC., as a
                               Guarantor

                               By: _________________________

                               Title:________________________

                               MXNET INC., as a Guarantor

                               By: _________________________

                               Title:________________________

                                       6
<PAGE>

                               IPC INFORMATION SYSTEMS ASIA PACIFIC, LIMITED,
                               as a Guarantor

                               By: _________________________

                               Title:________________________

                               IPC INFORMATION SYSTEMS CANADA, INC., as a
                               Guarantor

                               By: _________________________

                               Title:________________________

                               IXNET UK LIMITED, as a Guarantor

                               By: _________________________

                               Title:________________________

                               IPC INFORMATION SYSTEMS, as a Guarantor

                               By: _________________________

                               Title:________________________

                               IPC UK HOLDINGS, LTD., as a Guarantor

                               By: _________________________

                               Title:________________________

                               IPC UK SPC LIMITED, as a Guarantor

                               By: _________________________

                               Title:________________________

                                       7
<PAGE>

                               SATURN GLOBAL NETWORK SERVICES HOLDINGS
                               LIMITED, as a Guarantor

                               By: _________________________

                               Title:________________________

                               IXNET AUSTRALIA PTY LIMITED, as a Guarantor

                               By: _________________________

                               Title:________________________

                               IXNET HONG KONG LIMITED (f/k/a Saturn Global
                               Network Services (Hong Kong) Limited), as a
                               Guarantor

                               By: _________________________

                               Title:________________________

                               SATURN GLOBAL NETWORK SERVICES (JAPAN) LTD., as
                               a Guarantor

                               By: _________________________

                               Title:________________________

                               SATURN GLOBAL NETWORK SERVICES (SINGAPORE) PTE
                               LTD., as a Guarantor

                               By: _________________________

                               Title:________________________

                                       8

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