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                                                                    EXHIBIT 2.11

DATED                                                              27 April 2005

                  (1)   MITEL NETWORKS LIMITED

                  (2)   HIGHBRIDGE INTERNATIONAL LLC (as Security Agent)

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                             GUARANTEE AND INDEMNITY

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                                   MORGAN COLE
                                  Bradley Court
                                   Park Place
                                Cardiff CF10 3DP

                                    Ref: MDM

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THIS GUARANTEE AND INDEMNITY is made BY DEED and dated              April 2005

PARTIES:

(1)   MITEL NETWORKS LIMITED, a private company limited by shares incorporated
      in England and Wales under number 1309629 whose registered office is at
      Portskewett, Monmouthshire, NP26 5YR ("GUARANTOR")

(2)   HIGHBRIDGE INTERNATIONAL LLC ("SECURITY AGENT") as trustee for itself and
      the other Secured Parties.

RECITALS

      Whereas the Guarantor is a subsidiary of the Principal Debtor (as defined
      below) and has agreed to enter into this Guarantee to secure all of the
      monies, liabilities and obligations of the Principal Debtor (as defined
      below) owed to the Security Agent and the other Secured Parties pursuant
      to the Transaction Documents (as defined below).

AGREEMENT

1.    INTERPRETATION

 1.1   Unless the context otherwise requires or unless otherwise defined in this
       Guarantee, words and expressions shall have the same respective meanings
       that are given to them in the Transaction Documents.

 1.2   In this Guarantee the following expressions shall have the following
       meanings :-

       "CHARGE" means (i) the charge over book debts and cash at bank dated the
       date of this Guarantee (ii) the debenture dated the date of this
       Guarantee, and (iii) the charge over shares to be made after the date of
       this Guarantee, each made (or to be made, as the case may be) by the
       Guarantor in favour of the Security Agent, as the same may be amended,
       restated or supplemented from time to time.

       "COLLATERAL AGENCY AGREEMENT" means the collateral agency agreement dated
       the date hereof between, among others, the Security Agent, the Principal
       Debtor and the Noteholders (as defined therein);

       "PRINCIPAL DEBTOR" means Mitel Networks Corporation, a company
       incorporated under the laws of Canada.

       "SECURED PARTIES" means the Security Agent and the holders from time to
       time of the Notes and "SECURED PARTY" means any of them.

       "TRANSACTION DOCUMENTS" means the Securities Purchase Agreement among the
       Principal Debtor, the Security Agent and others dated on or about the
       date hereof, the senior secured convertible notes (the "NOTES") issued
       pursuant thereto, the Security Documents (as defined in the Notes), the
       Collateral Agency Agreement and the Registration Rights Agreement (as
       defined in the Notes).

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 1.3   References to "THIS GUARANTEE" include the indemnity in clause 3.3.

 1.4   References to clauses are to be construed as references to the clauses of
       this Guarantee.

 1.5   References to this Guarantee and to any provisions of this Guarantee or
       to any other document or agreement are to be construed as references to
       this Guarantee, those provisions or that document or agreement in force
       for the time being and as amended, varied, supplemented, substituted or
       novated from time to time.

 1.6   Words importing the singular are to include the plural and vice versa.

 1.7   References to a person are to be construed to include references to a
       corporation, firm, company, partnership, joint venture, unincorporated
       body of persons, individual or any state or any agency of a state,
       whether or not a separate legal entity.

 1.8   References to any person are to be construed to include that person's
       assigns or transferees or successors in title, whether direct or
       indirect.

 1.9   References to any statutory provision are to be construed as references
       to that statutory provision as amended, supplemented, re-enacted or
       replaced from time to time (whether before or after the date of this
       Guarantee) and are to include any orders, regulations, instruments or
       other subordinate legislation made under or deriving validity from that
       statutory provision.

 1.10  If any of the provisions of this Guarantee are or are found to be
       invalid, illegal or unenforceable in any respect under any law, the
       validity, legality and enforceability of the remaining provisions shall
       not in any way be affected or impaired

 1.11  The words "OTHER" and "OTHERWISE" are not to be construed ejusdem generis
       with any foregoing words where a wider construction is possible.

 1.12  References to liability are to include any liability whether actual,
       contingent, present or future.

 1.13  Headings are for ease of reference only and shall not affect the
       interpretation of this Guarantee.

2.    REPRESENTATIONS AND WARRANTIES BY THE GUARANTOR

 2.1   The Guarantor hereby represents and warrants to the Security Agent (for
       the benefit of itself and the other Secured Parties) that:

      2.1.1 the Guarantor is duly incorporated and is a validly existing company
            under the laws of its place of incorporation, has the capacity to
            sue or be sued in its own name and has power to carry on its
            business as now being conducted and to own its property and other
            assets;

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      2.1.2 the Guarantor has full power and authority to execute, deliver and
            perform its obligations under this Guarantee and under the Charge
            and no limitation on the powers of the Guarantor will be exceeded as
            a result of the Guarantor entering into this Guarantee or the
            Charge;

      2.1.3 the execution, delivery and performance by the Guarantor of this
            Guarantee and the Charge and the performance of its obligations
            under this Guarantee and the Charge have been duly authorized by all
            necessary corporate action and do not contravene or conflict with:

            (a)   the Guarantor's memorandum and articles of association or
                  other equivalent constitutional documents; or

            (b)   any resolutions of the shareholders or directors of the
                  Guarantor; or

            (c)   any existing law, statute, rule or regulation or any judgment,
                  decree or permit to which the Guarantor is subject; or

            (d)   the terms of any agreement or other document to which the
                  Guarantor is a party or which is binding upon it or any of its
                  assets;

      2.1.4 this Guarantee and the Charge are the legal, valid and binding
            obligations of the Guarantor and are enforceable against the
            Guarantor in accordance with their terms;

      2.1.5 except as disclosed in writing to the Security Agent, there are no
            actions, suits or proceedings pending or, to its knowledge,
            threatened (nor to the best of its knowledge is there any pending
            investigation) against or involving the Guarantor or any of its
            subsidiaries at law or in equity or before or by any federal, state,
            municipal or other governmental department, commission, board,
            bureau, agency or instrumentality, domestic or foreign, or before
            any arbitrator of any kind, which involves a reasonable possibility
            (so far as it can foresee) of either any material adverse change in
            the business, properties or financial condition of the Guarantor or
            of any adverse impairment of the value of the security granted or to
            be granted pursuant to the Charge and neither the Guarantor nor any
            of its subsidiaries is in default with respect to any judgment,
            order, writ, injunction, decree, rule or regulation of any court,
            arbitrator or federal, provincial, state, municipal or other
            governmental department, commission, board, bureau, agency or
            instrumentality which involves a reasonable possibility (so far as
            it can foresee) of either any material adverse change in the
            business, properties or financial condition of the Guarantor or of
            any adverse impairment of the value of the security granted or to be
            granted pursuant to the Charge.

 2.2   The Guarantor acknowledges that the Security Agent (for the benefit of
       itself and the other Secured Parties) has accepted this Guarantee and the
       Charge in full reliance on the representations and warranties set out in
       this clause 2, notwithstanding any investigation made by or on behalf of
       the Secured Parties. The representations and warranties made

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       by the Guarantor in this clause 2 for the benefit of the Secured Parties
       are material and shall survive the execution and delivery of this
       Guarantee and the Charge.

3.    GUARANTEE AND INDEMNITY

 3.1   In consideration of the Security Agent and the other Secured Parties
       entering into the Transaction Documents and making the facilities
       available to the Principal Debtor thereunder the Guarantor irrevocably
       and unconditionally undertakes the obligations and liabilities set out in
       clause 3.2.

 3.2   The Guarantor irrevocably and unconditionally guarantees on demand, the
       due and punctual performance and discharge of all obligations and
       liabilities of any kind whatsoever of the Principal Debtor to the Secured
       Parties and/or the Security Agent on their behalf in connection with or
       relating to the Transaction Documents, whether:

      3.2.1 present or future;

      3.2.2 actual or contingent; and/or

      3.2.3 owed by the Principal Debtor alone or jointly and/or severally with
            others

      (the "SECURED OBLIGATIONS").

 3.3   The Guarantor shall indemnify and keep indemnified the Security Agent
       (for the benefit of itself and the other Secured Parties) (to the extent
       not indemnified under the Transaction Documents or as otherwise
       indemnified under this Guarantee) on demand by the Security Agent against
       all losses, actions, claims, costs, charges, expenses and liabilities
       suffered or incurred by the Security Agent or any other Secured Party in
       relation to this Guarantee (including the costs, charges and expenses
       incurred in the enforcement of any of the provisions of this Guarantee or
       occasioned by any breach by the Guarantor of any of its obligations to
       the Security Agent under this Guarantee).

4.    SECURITY AGENT AND SECURED PARTY PROTECTIONS

 4.1   The Guarantor acknowledges and agrees that this Guarantee is and at all
       times shall be a continuing security and shall extend to cover the
       ultimate balance due at any time from the Principal Debtor to the
       Security Agent and the other Secured Parties under or in respect of any
       of the Transaction Documents and any of the transactions contemplated
       thereby, it being the intent of the Guarantor that its liability to the
       Secured Parties under this Guarantee shall be absolute and unconditional
       under all circumstances and shall not be discharged except by payment in
       full of all of the obligations and liabilities set out in clause 3.2.

 4.2   The Guarantor acknowledges and agrees that none of its liabilities under
       this Guarantee shall be reduced, discharged or otherwise adversely
       affected by:

      4.2.1 any variation, extension, discharge, compromise, dealing with,
            exchange or renewal of any right or remedy which the Security Agent
            or any other Secured

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            Party may now or hereafter have from or against the Principal Debtor
            and any other person in respect of any of the obligations and
            liabilities of the Principal Debtor and any other person under and
            in respect of the Transaction Documents;

      4.2.2 any act or omission by the Security Agent or any other person in
            taking up, perfecting or enforcing any security or guarantee from or
            against the Principal Debtor and any other person;

      4.2.3 any termination, amendment, variation, novation or supplement of or
            to the Transaction Documents;

      4.2.4 any grant of time, indulgence, waiver or concession to the Principal
            Debtor and any other person;

      4.2.5 any of the insolvency, bankruptcy, liquidation, administration,
            winding-up, incapacity, limitation, disability, the discharge by
            operation of law, and any change in the constitution, name and style
            of the Principal Debtor and any other person;

      4.2.6 any invalidity, illegality, unenforceability, irregularity or
            frustration of any actual or purported obligation of the Principal
            Debtor and any other person;

      4.2.7 any claim or enforcement of payment from the Principal Debtor and
            any other person;

      4.2.8 any act or omission which would have discharged or affected the
            liability of the Guarantor had it been a principal debtor instead of
            guarantor or indemnitor or by anything done or omitted by any person
            which but for this provision might operate to exonerate or discharge
            the Guarantor or otherwise reduce or extinguish its liability under
            this Guarantee in whole or in part;

      4.2.9 any lack of validity or enforceability of the Transaction Documents
            or any other agreement or instrument relating thereto.

 4.3   Primary obligation

      4.3.1 The obligations and liabilities expressed to be undertaken by the
            Guarantor under this Guarantee are those of primary obligor and not
            merely as a surety.

      4.3.2 The Security Agent shall not be obliged before taking steps to
            enforce any of its rights and remedies under this Guarantee (for the
            benefit of itself and the other Secured Parties):

            (a)   to take action or obtain judgment in any court against the
                  Principal Debtor and any other person;

            (b)   to make or file any claim in a bankruptcy, liquidation,
                  administration or insolvency of the Principal Debtor and any
                  other person; or

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            (c)   to make demand, enforce or seek to enforce any claim, right or
                  remedy against the Principal Debtor or any other person.

 4.4   Dealing with the Principal Debtor and Others

      4.4.1 The obligations and liabilities of the Guarantor hereunder shall not
            be released, discharged, limited or in any way affected by anything
            done, suffered or permitted by the Secured Parties in connection
            with any monies advanced by the Secured Parties to the Principal
            Debtor under the Transaction Documents or any security therefor,
            including any loss of or in respect of any security received by the
            Secured Parties from the Principal Debtor or others. It is agreed
            that the Secured Parties, without releasing, discharging, limiting
            or otherwise affecting in whole or in part the Guarantor's
            obligations and liabilities hereunder, may, without limiting the
            generality of the foregoing:

            (a)   grant time, renewals, extensions, indulgences, releases and
                  discharges to the Principal Debtor,

            (b)   increase or decrease the amount of the credit facilities
                  available to the Principal Debtor or amend, delete or add to
                  any terms or conditions of the Transaction Documents;

            (c)   take or abstain from taking securities or collateral from the
                  Principal Debtor or from perfecting securities or collateral
                  of the Principal Debtor;

            (d)   release, discharge, compromise or otherwise deal with (with or
                  without consideration) any and all collateral, mortgages or
                  other security given by the Principal Debtor or any third
                  party with respect to the obligations or matters contemplated
                  by the Transaction Documents;

            (e)   do, or omit to do, anything to enforce the payment or
                  performance of any of the obligations and liabilities set out
                  in clause 3.2 or take or abstain from taking security from the
                  Principal Debtor or any other person or to perfect or abstain
                  from perfecting any security interest;

            (f)   vary, compromise, exchange, renew, discharge, release,
                  subordinate, postpone, abandon or otherwise deal with any of
                  the obligations and liabilities set out in clause 3.2 or any
                  security interest;

            (g)   deal with or allow any creditor of the Principal Debtor or the
                  Guarantor or any other person to deal with goods or property
                  constituting collateral subject to any security interest;

            (h)   accept compromises from the Principal Debtor;

            (i)   apply all monies at any time received from the Principal
                  Debtor or from securities upon such part of the obligations
                  and liabilities set out in clause

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                  3.2 as the Secured Parties may see fit or change any such
                  application in whole or in part from time to time as the
                  Secured Parties may see fit; or

            (j)   otherwise deal with the Principal Debtor and all other persons
                  and securities as the Secured Parties may see fit.

      4.4.2 The Secured Parties shall not be bound or obliged to exhaust its
            recourse against the Principal Debtor or other persons or any
            securities, mortgage or collateral it may hold or take any other
            action before being entitled to payment from the Guarantor
            hereunder.

      4.4.3 Any account settled by or between the Secured Parties and the
            Principal Debtor with respect to the Transaction Documents shall in
            the absence of manifest error be accepted by the Guarantor as
            conclusive evidence that the balance or amount thereby appearing due
            to the Secured Parties is so due.

 4.5   No security

      4.5.1 The Guarantor warrants to the Security Agent that it has not taken
            or received, and agrees not to take, exercise or receive the benefit
            of any security or other right or benefit (whether by set-off,
            counterclaim, subrogation, indemnity, proof in liquidation or
            otherwise and whether from contribution or otherwise, all together
            'Rights') from or against any of the Principal Debtor or any other
            person in respect of any liability of or payment by the Guarantor
            under this Guarantee or otherwise in connection with this Guarantee
            other than the unsecured indemnity to be given by the Principal
            Debtor to the Guarantor in respect of this Guarantee.

      4.5.2 If any of such Rights is taken, exercised or received by the
            Guarantor, the Guarantor declares that such Rights and all monies at
            any time received or held in respect of such Rights shall be held by
            the Guarantor on trust for the Security Agent (for the benefit of
            itself and the other Secured Parties) for application in or towards
            the discharge of the liabilities of the Guarantor to the Security
            Agent and the other Secured Parties under this Guarantee.

      4.5.3 The Guarantor agrees that all other Rights and all monies from time
            to time held on trust by the Guarantor for the Security Agent (for
            the benefit of itself and the other Secured Parties) under or
            pursuant to clause 4.5.2 shall be transferred, assigned or, as the
            case may be, paid to the Security Agent, promptly following the
            Security Agent's demand.

 4.6   This Guarantee shall be in addition to and shall not affect or be
       affected by or merge with any other judgment, security, right or remedy
       obtained or held by the Security Agent (for the benefit of itself and the
       other Secured Parties) from time to time for the discharge and
       performance of any of the liabilities and obligations of the Principal
       Debtor to the Security Agent and the other Secured Parties.

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5. INTEREST

 5.1   The Guarantor agrees to pay interest to the Security Agent at the
       interest rate prescribed in the Notes after as well as before judgment on
       all sums demanded under this Guarantee from the date of the Security
       Agent's demand under this Guarantee or, if earlier, the date on which the
       relevant damages, losses, costs or expenses arose in respect of which
       such demand has been made, in each case until, but excluding, the date of
       actual payment.

 5.2   All such interest shall accrue on a day-to-day basis and shall be
       compounded in accordance with the Notes.

6. SUSPENSE ACCOUNT

 6.1   The Security Agent may place to the credit of a suspense account any
       monies received under or in connection with this guarantee in order to
       preserve the rights of the Security Agent (for the benefit of itself and
       the other Secured Parties) to prove for the full amount of all of its
       claims against any of the Principal Debtor and any other person.

 6.2   The Security Agent may at any time, apply any of the monies referred to
       in clause 6.1, in or towards satisfaction of any of the monies,
       obligations and liabilities the subject of this Guarantee as the Security
       Agent, in its absolute discretion, may from time to time conclusively
       determine.

7.    APPROPRIATION AND SUBROGATION

 7.1   The Guarantor shall not and may not direct the application by the
       Security Agent of any sums received by the Security Agent from the
       Guarantor under, or pursuant to, any of the terms of this Guarantee.

 7.2   The Guarantor shall have no right of subrogation in respect of payments
       made to the Secured Parties hereunder until such time as all obligations
       to the Secured Parties shall have been fully satisfied. In the case of
       the liquidation, winding-up or bankruptcy of the Principal Debtor
       (whether voluntary or involuntary) or in the event that the Principal
       Debtor shall make an arrangement or composition with its creditors, the
       Secured Parties shall have the right to rank for their full claims and to
       receive all dividends or other payments in respect thereof until their
       claims have been paid in full and the Guarantor shall continue to be
       liable to the Secured Parties up to the amount guaranteed (less any
       payments made by the Guarantor hereunder) for any balance which may be
       owing to the Secured Parties by the Principal Debtor. If (a) the
       Guarantor shall make payment to the Secured Parties of all or any part of
       the obligations and (b) all the obligations shall be paid in full, the
       Secured Parties will, at the Guarantor's request, forthwith, execute and
       deliver to the Guarantor appropriate documents, without recourse and
       without representation or warranty, necessary to evidence the transfer by
       subrogation to the Guarantor of its interest in the obligations resulting
       from such payment by the Guarantor.

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8.    NEW ACCOUNTS

 8.1   If this Guarantee ceases to be continuing for any reason whatsoever, then
       the Security Agent may open a new account or accounts in the name of the
       Principal Debtor.

 8.2   If the Security Agent does not open a new account or accounts pursuant to
       clause 8.1, it shall nevertheless be treated as if it had done so at the
       time that this Guarantee ceases to be continuing (whether by
       determination, calling in or otherwise) in relation to the Principal
       Debtor.

 8.3   As from that time, all payments made to the Security Agent by or on
       behalf of the Principal Debtor shall be credited or be treated as having
       been credited to the new account or accounts and shall not operate to
       reduce the amount for which this Guarantee guarantees available at that
       time nor shall the liability of the Guarantor under this Guarantee in any
       manner be reduced or affected by any subsequent transactions, receipts or
       payments into or out of any such accounts.

9.    DISCHARGE TO BE CONDITIONAL

 9.1   Any release, discharge or settlement between the Guarantor and the
       Security Agent (for the benefit of itself and the other Secured Parties)
       in relation to this Guarantee shall be conditional upon no right,
       security, disposition or payment to the Security Agent by any of the
       Guarantor and any other person being void, set aside or ordered to be
       refunded pursuant to any enactment or law relating to breach of duty by
       any person, bankruptcy, liquidation, administration, protection from
       creditors generally or insolvency or for any other reason.

 9.2   If any such right, security, disposition or payment is void or at any
       time so set aside or ordered to be refunded, the Security Agent (for the
       benefit of itself and the other Secured Parties) shall be entitled
       subsequently to enforce this Guarantee against the Guarantor as if such
       release, discharge or settlement had not occurred and any such security,
       disposition or payment had not been made.

10.   PAYMENTS AND TAXES

 10.1  All sums payable by the Guarantor under this Guarantee shall be paid to
       the Security Agent (for the benefit of itself and the other Secured
       Parties) in full without:

      10.1.1 any set-off, condition or counter-claim whatsoever; and

      10.1.2 free and clear of all deductions or withholdings whatsoever save
             only as may be required by law or regulation which in either case
             is binding on it.

 10.2  If any deduction or withholding is required by any law, practice or
       regulation (whether or not such practice or regulation has the force of
       law) in respect of any payment due from the Guarantor under this
       Guarantee or is in any event made, the relative sum payable by the
       Guarantor shall be increased so that, after making the minimum deduction
       or withholding so required, the Guarantor shall pay to the Security Agent
       for

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      the benefit of itself and the other Secured Parties and the Security Agent
      and the Secured Parties shall receive and be entitled to retain on the due
      date for payment a net sum at least equal to the sum which it would have
      received had no such deduction or withholding been required to be or had
      in fact been made.

11.   DEMANDS AND NOTIFICATION BINDING

 11.1  Any demand, notification or certificate given by the Security Agent
       specifying amounts due and payable under or in connection with any of the
       provisions of this Guarantee shall, in the absence of manifest error, be
       conclusive and binding on the Guarantor.

12.   COSTS

 12.1  The Guarantor shall, on demand and on a full indemnity basis, pay to the
       Security Agent (for the benefit of itself and the other Secured Parties)
       the amount of all costs and expenses (including legal and out-of-pocket
       expenses and any Value Added Tax on such costs and expenses) which the
       Security Agent incurs in connection with:-

      12.1.1 the preparation, negotiation, execution and delivery of this
             Guarantee;

      12.1.2 any actual or proposed amendment, variation, supplement, waiver or
             consent under or in connection with this Guarantee;

      12.1.3 any discharge or release of this Guarantee;

      12.1.4 the preservation or exercise (or attempted preservation or
             exercise), and the enforcement (or attempted enforcement) of, any
             rights under or in connection with, this Guarantee.

13.   SET-OFF

 13.1  The Security Agent (for the benefit of itself and the other Secured
       Parties) and each other Secured Party may, following a demand under this
       Guarantee but without notice to the Guarantor, apply any credit balance
       which is at any time held by any office or branch of the Security Agent
       for the account of the Guarantor in or towards satisfaction of any sum
       then due and payable from the Guarantor under this Guarantee.

 13.2  For the purposes of exercising any rights under this clause, or any
       rights under the general law, any Secured Party may convert or translate
       all or any part of such credit balance into another currency applying a
       rate which in its opinion fairly reflects the relative prevailing rates
       of exchange.

 13.3  No Secured Party is obliged to exercise any of its rights under this
       clause, which shall be without prejudice and in addition to any rights
       under the general law.

 13.4  In this clause "rights under the general law" means any rights of
       set-off, combination or consolidation of accounts, lien or similar tight
       which any Secured Party has under any applicable law.

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14.   NOTICES

 14.1  A demand notice or other communication to the Guarantor in connection
       with this Guarantee:

      14.1.1 shall be in writing and;

      14.1.2 shall be left at or sent by facsimile or prepaid ordinary post
             (airmail if posted to a place outside the United Kingdom) to the
             Guarantor addressed to the person at the address identified with
             its signature below.

 14.2  A demand notice or other communication shall take effect from the time it
       is received (or if earlier the time it is deemed to be received in
       accordance with clause 14.3) unless a later time is specified in it.

 14.3  A letter or facsimile is deemed to be received:-

      14.3.1 in the case of a posted letter unless actually received earlier on
             the second (fifth if posted to a place outside the United Kingdom)
             day after posting; and

      14.3.2 in the case of facsimile on production of a transmission report
             from the machine from which the facsimile was sent which indicates
             that the facsimile was sent in its entirety to the facsimile number
             of the recipient.

15.   TRANSFERS

 15.1  This Guarantee is freely assignable or transferable by the Security Agent
       (for the benefit of itself and the other Secured Parties).

 15.2  The Guarantor may not assign any of its rights and may not transfer any
       of its obligations under this Guarantee or enter into any transaction
       which would result in any of those rights or obligations passing to
       another person without the prior written consent of the Security Agent,
       which may be withheld in the sole discretion of the Security Agent.

 15.3  CURRENCY INDEMNITY

      If, under any applicable law or regulation or pursuant to a judgment or
      order being made or registered against the Guarantor or the liquidation of
      the Guarantor or without limitation for any other reason, any payment
      under or in connection with this Guarantee is made or falls to be
      satisfied in a currency ("PAYMENT CURRENCY") other than the currency in
      which such payment is expressed to be due under or in connection with this
      Guarantee ("CONTRACTUAL CURRENCY") then, to the extent that the amount of
      such payment actually received by the Security Agent, when converted into
      the contractual currency at the rate of exchange falls short of the amount
      due under or in connection with this Guarantee, the Guarantor, as a
      separate and independent obligation, shall indemnify and hold harmless the
      Security Agent against the amount of such shortfall. For the purposes of
      this clause, "RATE OF EXCHANGE" means the rate at which the Security Agent
      is able on

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                                     - 12 -

      or about the date of such payment to purchase, in accordance with its
      normal practice, the contractual currency with the payment currency and
      shall take into account (and the Guarantor shall be liable for) any
      premium and other costs of exchange including any taxes or duties incurred
      by reason of any such exchange.

16.   MISCELLANEOUS

 16.1  No delay or omission on the part of the Security Agent in exercising any
       right or remedy under this Guarantee shall impair that right or remedy or
       operate as or be taken to be a waiver of it, nor shall any single partial
       or defective exercise of any such right or remedy preclude any other or
       further exercise under this Guarantee of that or any other right or
       remedy.

 16.2  The Security Agent's rights under-this Guarantee are cumulative and not
       exclusive of any rights provided by law and may be exercised from time to
       time and as often as the Security Agent deems expedient.

 16.3  Any waiver by the Security Agent of any terms of this Guarantee, or any
       consent or approval given by the Security Agent under it, shall only be
       effective if given in writing and then only for the purpose and upon the
       terms and conditions, if any, on which it is given.

 16.4  If at any time any one or more of the provisions of this Guarantee is or
       becomes illegal, invalid or unenforceable in any respect under any law of
       any jurisdiction, neither the legality, validity and enforceability of
       the remaining provisions of this Guarantee nor the legality, validity or
       enforceability of such provision under the law of any other jurisdiction
       shall be in any way affected or impaired as a result.

 16.5  The Guarantor shall at all times do, execute, acknowledge and deliver or
       cause to be done, executed, acknowledged or delivered all such further
       acts, deeds, transfers, assignments and assurances as the Security Agent
       may reasonably require in order to give effect to the provisions of this
       Guarantee and the provisions of the Charge.

 16.6  This Guarantee may be executed in more than one counterpart each of which
       shall constitute an original.

17.   LANGUAGE

      All notices demands or communications under or in connection with this
      Guarantee shall be in English.

18.   LAW AND JURISDICTION

19.1  This Guarantee shall be governed by and construed in accordance with the
      laws of England and Wales.

19.2  The Guarantor irrevocably agrees for the benefit of the Security Agent
      that the courts of England and/or any of the federal or State courts
      sitting in The City of New York,

<PAGE>

                                     - 13 -

      Borough of Manhattan will have jurisdiction to hear and determine any
      suit, action or proceeding, and to settle any disputes which may arise out
      of, or in connection with, this Guarantee and, for that purpose,
      irrevocably submits to the jurisdiction of such courts.

19.3  The Guarantor irrevocably waives any objection which it might now or
      hereafter have to any of the courts referred to in clause 19.2 being
      nominated as the forum to hear and determine any suit, action or
      proceeding, and to settle any disputes which may arise out of, or in
      connection with, this Guarantee and agrees not to claim that any such
      court is not a convenient or inappropriate forum.

19.4  The submission to the jurisdiction of the courts referred to in clause
      19.2 will not (and is not to be construed so as to) limit the right of the
      Security Agent to take proceedings against the Guarantor in any other
      court of competent jurisdiction, nor will the taking of proceedings in any
      one or more jurisdictions preclude the taking of proceedings in any other
      jurisdiction, whether concurrently or not.

19.5  The Guarantor hereby consents in respect of any legal action or proceeding
      arising out of, or in connection with, this Guarantee, to the giving of
      any relief, or the issue of any process in connection with such action or
      proceeding including, without limitation, the making, enforcement or
      execution against any property whatsoever (irrespective of its use or
      intended use) of any order or judgment which may be made or given in such
      action or proceeding.

19.6  To the extent that the Guarantor may in any jurisdiction claim for itself
      or its assets, immunity from suit, execution, attachment (whether in aid
      of execution, before judgment or otherwise) or other legal process and, to
      the extent that in any such jurisdiction there may be attributed to itself
      or its assets such immunity (whether or not claimed), the Guarantor hereby
      irrevocably agrees that it will not claim, and hereby irrevocably waives,
      such immunity to the full extent permitted by the law of such
      jurisdiction.

19.   SECURITY AGENT

 19.1  The relevant provisions of the Transaction Documents shall apply to the
       Security Agent's rights, obligations, powers and duties under this
       Guarantee as if set out in this Guarantee in full.

20.   TERMINATION

21.1  This Guarantee is a continuing security, and shall not terminate or be
      discharged until the earlier of (a) performance and indefeasible payment
      in full of all of the Secured Obligations and (b) the date on which a
      Qualified IPO (as defined in the Notes) is consummated.

21.   RIGHTS OF THIRD PARTIES

      Save as expressly provided to the contrary in any Transaction Document:

<PAGE>

IN WITNESS whereof this Guarantee and Indemnity has been executed as a Deed the
day and year first before written.

EXECUTED as a Deed (but not delivered
until the date hereof by MITEL
NETWORKS LIMITED and signed by
two directors or a director and the secretary

                                      Director /s/ [ILLEGIBLE]
                                               ------------------------

                                      Director /s/ Paul Butcher
                                               ------------------------

NOTICE DETAILS

        Address:    Mitel Business Park
                    Portskewett
                    Caldicot
                    Gwent NP26 5YR

        Fax No.:    0870 909 4040

        Tel. No.:   0870 909 2020

        Attention:  Chris Crane

EXECUTED as a Deed (but not delivered           HIGHBRIDGE INTERNATIONAL LLC
until the date hereof by the SECURITY
AGENT acting by its duly authorized             BY: HIGHBRIDGE CAPITAL
signatories                                     MANAGEMENT, LLC


                                        By: ___________________________________
                                            Name: Ari J. Storch
                                            Title: Managing Director

<PAGE>

IN WITNESS whereof this Guarantee and Indemnity has been executed as a Deed the
day and year first before written.

EXECUTED as a Deed (but not delivered
until the date hereof by MITEL
NETWORKS LIMITED and signed by two directors or
a director and the secretary

                                      Director _________________________________

                                 Director/Secretary ____________________________

NOTICE DETAILS

        Address:        Mitel Business Park
                        Portskewett
                        Caldicot
                        Gwent NP26 5YR

        Fax No.:        0870 909 4040

        Tel. No.:       0870 909 2020

        Attention:      Chris Crane

EXECUTED as a Deed (but not delivered           HIGHBRIDGE INTERNATIONAL LLC
until the date hereof by the SECURITY
AGENT acting by its duly authorized             BY: HIGHBRIDGE CAPITAL
signatories                                     MANAGEMENT, LLC

                                        By: /s/ Adam J. Chill
                                            ------------------------------------
                                            Name: Adam J. Chill
                                            Title: Managing Director