<PAGE>
                                                                 (JPMORGAN LOGO)

                                                                     Exhibit 4.1

                     CAP/FLOOR COLLAR TRANSACTION (REVISION)

 This confirmation, dated 03 October 2005, supersedes any previous confirmations
    received referencing JPM REFERENCE NUMBER 200005065393 and 200005065440.

The purpose of this letter agreement is to confirm the terms and conditions of
the Transaction entered into between:

                            JPMORGAN CHASE BANK. N.A.
                                  ("JPMorgan")

                                       and

                           MITEL NETWORKS CORPORATION
                              (the "Counterparty")

on the Trade Date and identified by the JPMorgan Deal Number specified below
(the "Transaction"). This letter agreement constitutes a "Confirmation" as
referred to in the Master Agreement specified below, and supersedes any previous
confirmation or other writing with respect to the transaction described below.

The definitions and provisions contained in the 2000 ISDA Definitions (the
"Definitions"), as published by the international Swaps and Derivatives
Association, Inc. are incorporated into this Confirmation. In the event of any
inconsistency between those definitions and provisions and this Confirmation,
this Confirmation will govern.

If JPMORGAN CHASE BANK, N.A. ("JPMorgan") and MITEL NETWORKS CORPORATION (the
"Counterparty") are not yet parties to an ISDA Master Agreement, the parties
agree that this Transaction will be documented under a master agreement to be
entered into, on or before October 11, 2005, on the basis of the printed form of
the 2002 Master Agreement published by the International Swap and Derivatives
Association, Inc. ("ISDA"), together with such changes as shall be agreed
between the parties (the "Master Agreement"). Upon execution and delivery by the
parties of the Master Agreement, this Confirmation shall supplement, form a part
of, and be subject to such Master Agreement. Until the parties execute and
deliver the Master Agreement, this Confirmation shall supplement, form a part
of, and be subject to the printed form of 2002 Master Agreement published by
ISDA, as if the parties had executed that agreement in such form (but without
any Schedule except for the election of the laws of the State of New York as the
governing law and US Dollars as the Termination Currency) on the Trade Date of
this Transaction. If such 2002 Master Agreement is not executed by the parties
on or before October 11, 2005, it shall constitute an Additional Termination
Event under the Master Agreement, in respect of which both parties are Affected
Parties.


                                                                     Page 1 of 1
<PAGE>
                                                                 (JPMORGAN LOGO)

The terms of the particular Cap/Floor Collar Transaction to which this
Confirmation relates are as follows:

A. TRANSACTION DETAILS

<TABLE>
<S>                                  <C>
JPMorgan Deal Number(s):             2000005065440

Notional Amount:                     USD 55,000,000.00

Trade Date:                          26 September 2005

Effective Date:                      01 November 2005

Termination Date:                    01 November 2007, subject to adjustment in
                                     accordance with the Modified Following
                                     Business Day Convention

FIXED AMOUNT:

Fixed Rate Payer:                    Counterparty

Premium Amount:                      USD 0.00

Fixed Rate Payer Payment Date:       N/A

FLOATING AMOUNTS (1):

Floating Rate Payer:                 JPMorgan

Cap Rate:                            5.27 percent

Floating Rate Payer Payment Dates:   Each 01 May and 01 November from and
                                     including 01 May 2006 to and including the
                                     Termination Date, subject to adjustment in
                                     accordance with the Modified Following
                                     Business Day Convention and there will be
                                     an adjustment to the Calculation Period

Floating Rate Option:                USD-LIBOR-BBA

Designated Maturity:                 3 Months

Spread:                              None

Floating Rate Day Count Fraction:    Actual/360

Reset Dates:                         Each 01 January, 01 April, 01 July. and 01
                                     October beginning with October 1, 2005,
                                     subject to the Previous Business Day
                                     Convention

Compounding:                         Inapplicable

Business Days:                       New York, London, Ottawa
</TABLE>


                                                                     Page 2 of 2
<PAGE>
                                                                 (JPMORGAN LOGO)

FLOATING AMOUNTS (II):

<TABLE>
<S>                                  <C>
Floating Rate Payer:                 Counterparty

Floor Rate:                          4.00000 percent

Floating Rate Payer Payment Dates:   Each 01 May and 01 November from and
                                     including 01 May 2006 to and including the
                                     Termination Date, subject to adjustment in
                                     accordance with the Modified Following
                                     Business Day Convention and there will be
                                     an adjustment to the Calculation Period

Floating Rate Option:                USD-LIBOR-BBA

Designated Maturity:                 3 Months

Spread:                              None

Floating Rate Day Court Fraction:    Actual 360

Reset Dates:                         Each 01 January, 01 April, 01 July, and 01
                                     October beginning with 01 October 2005,
                                     subject to the Previous Business Day
                                     Convention

Compounding:                         Inapplicable

Business Days:                       New York, London, Ottawa

Calculation Agent:                   JPMorgan, unless otherwise stated in the
                                     Agreement.

B. ACCOUNT DETAILS

Payments to JPMorgan in USD:         JPMORGAN CHASE BANK NA
                                     JPMORGAN CHASE BANK NA
                                     BIC: CHASUS33XXX
                                     AC No: 099997979

Payments to Counterparty in USD:     As per your standard settlement
                                     instructions.

C. OFFICES

JPMorgan:                            NEW YORK

Counterparty:                        OTTAWA
</TABLE>


                                                                     Page 3 of 3
<PAGE>
                                                                 (JPMORGAN LOGO)

D. GOVERNING LAW

The laws of the State of New York provided however that upon execution of the
Master Agreement this Confirmation shall be governed by the law governing such
Master Agreement.

E. DOCUMENTS TO BE DELIVERED

Each party shall deliver to the other, at the time of its execution of this
Confirmation, evidence of the incumbency and specimen signature of the person(s)
executing this Confirmation, unless such evidence has been previously supplied
and remains true and in effect.

F. RELATIONSHIP BETWEEN PARTIES

Each party will be deemed to represent to the other party on the date on which
it enters into a Transaction that (absent a written agreement between the
parties that expressly imposes affirmative obligations to the contrary for that
Transaction):

(a) Non-Reliance. It is acting for its own account, and it has made its own
independent decisions to enter into that Transaction and as to whether that
Transaction is appropriate or proper for it based upon its own judgment and upon
advice from such advisers as it has deemed necessary. It is not relying on any
communication (written or oral) of the other party as investment advice or as a
recommendation to enter into that Transaction; it being understood that
information and explanations related to the terms and conditions of a
Transaction shall not be considered investment advice or a recommendation to
enter into that Transaction. No communication (written or oral) received from
the other party shall be deemed to be an assurance or guarantee as to the
expected results of that Transaction.

(b) Assessment and Understanding. It is capable of assessing the merits of and
understanding (on its own behalf or through independent professional advice),
and understands and accepts, the terms, conditions and risks of that
Transaction. It is capable of assuming, and assumes the risks of that
Transaction.

(c) Status of Parties. The other party is not acting as a fiduciary for or an
adviser to it in respect of that Transaction.


                                                                     Page 4 of 4
<PAGE>
                                                                 (JPMORGAN LOGO)

Please confirm that the foregoing correctly sets forth the terms of our
agreement by executing a copy of this Confirmation and returning it to us or by
sending to us a letter, telex or facsimile substantially similar to this letter,
which letter, telex or facsimile sets forth all material terms of the
Transaction to which this Confirmation relates and indicates agreement to those
terms. When referring to this Confirmation, please indicate: JPMorgan Deal
Number(s): 2000005065440.

JPMorgan Chase Bank, N.A.


/s/ Cathy Stutz
-------------------------------------
Name: Cathy Stutz
Title: Associate

Accepted and confirmed as of the date
first written:
MITEL NETWORKS


/s/ D. McCarthy
-------------------------------------
Name: D. McCarthy
Title: Treasurer
Your reference number:
                       --------------


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