EXECUTION COPY







                                   SONUS CORP.


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                              AMENDED AND RESTATED
                                WARRANT AGREEMENT

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                  WARRANTS TO PURCHASE 2,000,000 COMMON SHARES

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         THIS AMENDED AND RESTATED WARRANT AGREEMENT (this "Agreement") dated as
of  October 1, 1999 is made and  entered  into by and  between  Sonus  Corp.,  a
corporation  continued and existing  under the laws of Yukon  Territory,  Canada
(the  "Company"),  and  Warburg,  Pincus  Ventures,  L.P.,  a  Delaware  limited
partnership (the "Warrantholder").

         Subject to the terms and  conditions  hereof,  pursuant to a Securities
Purchase  Agreement  dated as of October 1, 1999, by and between the Company and
the Warrantholder (the "Securities Purchase  Agreement"),  the Company agrees to
(a) amend and  restate,  as  hereinafter  described,  the terms of the  warrants
described in and issued pursuant to that certain  Warrant  Agreement dated as of
December  24,  1997,  by and  between  the  Company  and the  Warrantholder,  as
represented  by Warrant  Certificate  No. W-1 of the Company dated  December 24,
1997 (the "Old Warrant  Certificate");  (b) cancel the Old Warrant  Certificate;
and (c) issue to the Warrantholder, Amended and Restated Warrant Certificate No.
W-1 of the  Company,  the  form of  which  is  attached  hereto  as  Exhibit  1,
representing  warrants  (the  "Warrants")  to  purchase  up to an  aggregate  of
2,000,000 common shares without par value of the Company (the "Common  Shares"),
at the Warrant Price (as hereinafter defined), subject to adjustment pursuant to
Section 6 hereof.  As used herein (i) the term "Shares"  shall mean,  unless the
context  otherwise  requires,  collectively  the  Common  Shares  issuable  upon
exercise of the Warrants  together with any other  securities or other  property

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issuable upon such exercise as provided in Section 6 of this Agreement; (ii) the
term "Warrants" shall include any and all warrants  outstanding pursuant to this
Agreement,  including those  evidenced by a certificate or  certificates  issued
upon division,  exchange or substitution  pursuant to this Agreement;  (iii) the
term "Warrant Price" shall mean the price per Share at which Shares shall at any
time be  purchasable  upon  exercise of the  Warrants,  such price to equal U.S.
$6.75, subject to adjustment pursuant to Section 6 hereof,  provided that if the
Series A Amendment  Filing Date has not  occurred on or prior to March 31, 2000,
then from and after March 31, 2000, such price shall equal U.S.  $4.00,  subject
to  adjustment  pursuant  to  Section  6  hereof;  and (iv) the term  "Series  A
Amendment  Filing  Date"  shall  mean the date  upon  which  the  amendment  and
restatement  of the  terms  of the  Series  A  Convertible  Shares,  in the form
attached to the Securities Purchase Agreement as Exhibit B, shall have occurred,
as  preceded  by the  passing  of  resolutions  by a  majority  of not less than
two-thirds of the votes cast by the holders of the Common  Shares,  the Series A
Convertible Shares and Series B Convertible  Shares of the Company,  each voting
separately  as a  class,  as  evidenced  by (1) a  duly  executed  report  of an
inspector  of election,  (2) a copy of the  articles of  amendment  amending the
terms  of the  Series  A  Convertible  Shares,  certified  by the  registrar  of
Corporations  of the  Yukon  Territory  and (3) an  opinion  of  counsel  to the
Company,  addressed to the Investor,  in the form attached  hereto as Exhibit 4,
and such other  documentation as the Investor may reasonably  request;  provided
that no Series A Amendment  Filing Date shall occur after March 31, 2000.  Terms
which are  capitalized but not defined herein shall have the same meanings as in
the Securities Purchase  Agreement.  Any amounts herein referencing share prices
or numbers of shares shall be subject to appropriate adjustments in the event of
any stock splits, consolidations or the like.

         For the purpose of defining  the terms and  provisions  of the Warrants
and the  respective  rights and  obligations  thereunder,  the  Company  and the
Warrantholder, for value received, hereby agree as follows:

         Section 1.  Restrictions on Transfer and Form of Warrants.

         1.1.  Registration.  Certificates  evidencing  the  Warrants  shall  be
numbered and shall be  registered  on the books of the Company  when issued,  in
accordance with Yukon Territory corporate practice.

         1.2. Restriction on Transfer of the Warrants. The Warrants shall not be
transferable  and  may  not  be  sold,   assigned,

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hypothecated or otherwise  transferred by the Warrantholder  without the express
written consent of the Company,  such consent not to be  unreasonably  withheld.
Any  transferee  permitted  under this Section 1.2 shall  acquire  title to such
transferred Warrants and to all rights represented thereby.

         1.3. Form of Warrants.  The form of certificate evidencing the Warrants
shall be substantially as set forth in Exhibit 1 hereto. Certificates evidencing
the Warrants  shall be executed on behalf of the Company by its  President or by
any Vice  President,  shall be attested  to by its  Secretary  or any  Assistant
Secretary, and shall be dated as of the date of execution thereof.

         1.4.  Legends on Warrants  and Common  Shares.  The  Warrants,  and the
Shares issuable upon the exercise  thereof,  have not been registered  under the
Securities Act of 1933, as amended (the "Securities  Act"). Each certificate for
the Warrants shall bear the following legend:

                  "THE WARRANTS REPRESENTED BY THIS CERTIFICATE,  AND THE COMMON
                  SHARES ISSUABLE UPON EXERCISE OF SUCH WARRANTS,  HAVE NOT BEEN
                  REGISTERED  UNDER THE UNITED STATES  SECURITIES ACT OF 1933 OR
                  THE  SECURITIES  LAWS OF ANY STATE OF THE UNITED STATES OR ANY
                  PROVINCE OF CANADA. SUCH WARRANTS MAY NOT BE SOLD, OFFERED FOR
                  SALE,   ASSIGNED,   EXCHANGED,   PLEDGED  OR  HYPOTHECATED  OR
                  OTHERWISE  TRANSFERRED,  IN ANY MANNER, AND SUCH COMMON SHARES
                  MAY NOT BE OFFERED FOR SALE, SOLD,  PLEDGED OR HYPOTHECATED OR
                  TRANSFERRED IN THE ABSENCE OF SUCH  REGISTRATION OR AN OPINION
                  OF COUNSEL,  REASONABLY  SATISFACTORY TO THE COMPANY,  THAT AN
                  EXEMPTION FROM SUCH  REGISTRATION  IS AVAILABLE.  THE WARRANTS
                  REPRESENTED  BY THIS  CERTIFICATE  MAY NOT BE TRADED IN CANADA
                  EXCEPT AS PERMITTED BY RELEVANT CANADIAN SECURITIES LAWS."

Each certificate for the Shares shall bear the following legend:

                  "THE COMMON SHARES  REPRESENTED BY THIS  CERTIFICATE  HAVE NOT
                  BEEN REGISTERED UNDER THE UNITED STATES SECURITIES ACT OF 1933
                  OR THE  SECURITIES  LAWS OF ANY STATE OF THE UNITED  STATES OR
                  ANY  PROVINCE  OF  CANADA  AND  MAY  NOT  BE  SOLD,  ASSIGNED,
                  EXCHANGED  OR

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<PAGE>

                  OTHERWISE TRANSFERRED,  IN THE ABSENCE OF SUCH REGISTRATION OR
                  AN OPINION OF COUNSEL, REASONABLY SATISFACTORY TO THE COMPANY,
                  THAT AN EXEMPTION  FROM SUCH  REGISTRATION  IS AVAILABLE  THIS
                  CERTIFICATE MAY NOT CONSTITUTE 'GOOD DELIVERY' IN SATISFACTION
                  OF  A  TRADE  MADE  ON  A  STOCK  EXCHANGE  IN  CANADA.   THIS
                  CERTIFICATE IS NOT TRANSFERABLE IN CANADA UNTIL MARCH 30, 2000
                  EXCEPT   PURSUANT  TO  AN   EXEMPTION   FROM  THE   PROSPECTUS
                  REQUIREMENTS    CONTAINED   IN   THE   APPLICABLE   SECURITIES
                  LEGISLATION."

         Any certificate  issued at any time in exchange or substitution for any
certificate bearing such legend (except a new certificate issued upon completion
of  a  public  distribution  pursuant  to a  registration  statement  under  the
Securities Act of the Common Shares represented  thereby) shall also bear a like
legend unless, in the opinion of counsel reasonably satisfactory to the Company,
the  securities   represented   thereby  need  no  longer  be  subject  to  such
restrictions.

         Section 2.  Term of Warrants; Exercise of Warrants.

                  (a) Subject to the terms of this Agreement,  the Warrantholder
shall  have the  right,  at any time and from  time to time  during  the  period
commencing at 9:00 a.m.,  Pacific Time, on October 1, 1999,  (the  "Commencement
Date")  and  ending  at 5:00  p.m.,  Pacific  Time,  on  October  1,  2004  (the
"Termination  Date") to purchase from the Company up to the number of fully paid
and nonassessable  Shares which the Warrantholder may at the time be entitled to
purchase  pursuant  to this  Agreement,  upon  surrender  to the  Company at its
principal  office of the  certificates  evidencing the Warrants to be exercised,
with the purchase form, in the form attached hereto as Exhibit 2, duly completed
and  signed,  and upon  payment  to the  Company  of an  amount  (the  "Exercise
Payment")  equal to the Warrant  Price  multiplied by the number of Shares being
purchased  pursuant to such exercise,  payable in cash, by certified or official
bank check, or by wire transfer.

                  (b) At any time  subsequent  to the first  anniversary  of the
Commencement  Date,  in lieu of  exercising  the Warrants as provided in Section
2(a) above,  and subject to all  applicable  law and all  applicable  regulatory
approvals, limitations and restrictions, the Warrantholder may elect to receive,
without any cash payment,  a number of Shares equal to the value (as  determined
below) of any or all of the Warrants held of record by

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<PAGE>

the Warrantholder,  upon surrender to the Company at its principal office of the
certificates  evidencing such Warrants, with the attached cashless exercise form
attached  hereto as Exhibit 3 duly  completed  and  signed,  in which  event the
Company shall issue to the  Warrantholder  a number of Shares computed using the
following formula:

                  X = Y(A-B)
                                        A

where

                  X = the number of Common Shares to be issued  pursuant to this
                      Section 2(b).

                  Y = the number of Common Shares  issuable upon exercise of the
                      surrendered Warrants.

                  A = the average of the Market  Prices of the Common Shares for
                      the sixty (60)  calendar  days  immediately  preceding the
                      date  upon   which   the   certificates   evidencing   the
                      surrendered  Warrants  are  received by the Company at its
                      principal office.

                  B = the Warrant Price on such date.

         For all purposes of this  Agreement  the term "Market  Price" as of any
specified  date shall mean:  (i) if the Common Shares are listed or admitted for
trading on one or more United States national  securities  exchanges,  the daily
closing  price for the Common  Shares on the  principal  exchange  in the United
States on which the Common Shares are listed;  (ii) if the Common Shares are not
listed  or  admitted  for  trading  on any  United  States  national  securities
exchange,  the daily closing price for the Common Shares on the Nasdaq  National
or Nasdaq Small-Cap Market ("Nasdaq"); (iii) if the Common Shares are not listed
or admitted for trading on a United States  national  securities  exchange or on
Nasdaq,  the daily closing  price of the Common  Shares on the  principal  stock
exchange in Canada on which the Common  Shares are listed  (expressed  in United
States  dollars  based  upon the noon  buying  rate in New York  City for  cable
transfers in Canadian  dollars as certified for customs  purposes by the Federal
Reserve Bank of New York);  (iv) if the Common Shares are not listed or admitted
to  trading  on any United  States  national  or  Canadian  national  securities
exchange or on Nasdaq,  the average of the  reported bid and asked prices on the
trading day preceding such date in the  over-the-counter  market as furnished by
the National

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<PAGE>

Quotation Bureau,  Inc., or, if such firm is not then engaged in the business of
reporting such prices, as furnished by any member of the National Association of
Securities  Dealers,  Inc. selected by the Company;  or (y) if the Common Shares
are not publicly traded,  the Market Price for such day shall be the fair market
value thereof determined jointly by the Company and the Warrantholder; provided,
however,  that if such parties are unable to reach agreement within a reasonable
period  of time,  the  Market  Price  shall be  determined  in good  faith by an
independent  investment  banking  firm  selected  jointly by the Company and the
Warrantholder or, if that selection cannot be made within an additional 15 days,
by an independent  investment banking firm selected by the American  Arbitration
Association in accordance with its rules.

                  (c)  The Company may, at any time, elect to force the exercise
of the  Warrants  by the  Warrantholder  subject to the terms of this  Agreement
provided that the Company shall have  satisfied all of the following  conditions
prior to the date of such election by the Company:

                       (i) the  Common  Shares  are listed on the New York Stock
         Exchange, the American Stock Exchange or the Nasdaq National Market;

                       (ii) the  Common  Shares are traded on the New York Stock
         Exchange,  the American Stock Exchange or the Nasdaq National Market at
         a Market Price greater than U.S. $8.00 per share for the 10 consecutive
         trading days immediately preceding the date of such election; and

                       (iii) The Company's net income  (excluding profit or loss
         on disposal of a significant  part of the Company's  assets or separate
         segment thereof,  gains on restructuring  payables,  gains or losses on
         the extinguishment of debt, expropriations of property, gains or losses
         that are the direct  result of a major  casualty,  or  one-time  losses
         resulting from  prohibitions  under a newly-enacted  law or regulation)
         for the three  consecutive  fiscal quarters ended  immediately prior to
         the date of such election, as reported in or derived from its quarterly
         or annual reports filed with the  Securities  and Exchange  Commission,
         before  income taxes,  dividends on the Company's  Series A Convertible
         Preferred   Shares   and   Series  B   Convertible   Preferred   Shares
         (collectively,  the "Convertible  Shares") and amortization of goodwill
         and covenants  not to compete for such  quarterly  periods,  shall have
         averaged at least U.S.  $0.35 per fully diluted Common Share per fiscal
         quarter, provided, however,

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<PAGE>

         that in making  such  calculation,  the  Common  Shares  issuable  upon
         exercise of the Warrants  shall be excluded but Common Shares  issuable
         upon the conversion of the Convertible Shares shall not.

The foregoing  conditions (i), (ii) and (iii) shall  hereinafter be collectively
referred to as the "Triggering  Conditions." All references to per share amounts
or prices  with  respect to the  Triggering  Conditions  shall be  appropriately
adjusted for any stock splits, consolidations or the like.

         The  Company  shall  give the  Warrantholder  written  notice  that the
Triggering  Conditions have been satisfied and that the Company intends to force
the exercise of the Warrants.  In this event,  the Termination Date shall be the
date ten (10) business days after such notice shall be effectively  delivered to
the Warrantholder as provided in Section 10 of this Agreement.

         In the event of a forced exercise of Warrants  pursuant to this Section
2(c), in lieu of exercising the Warrants as provided in Section 2(a) above,  and
subject  to  all  applicable  law  and  all  applicable   regulatory  approvals,
limitations and restrictions,  the  Warrantholder may elect to receive,  without
any cash payment, a number of Shares equal to the value (as determined below) of
any or all of the Warrants held of record by the  Warrantholder,  upon surrender
to the  Company at its  principal  office of the  certificates  evidencing  such
Warrants,  with the attached  cashless  exercise form thereof duly completed and
signed,  in which event the Company shall issue to the holder a number of Shares
computed using the formula set forth in Section 2(b) except the term "A" in such
formula, the Market Price of the Common Shares, shall be calculated based on the
ten (10) trading days  immediately  preceding the date on which the certificates
evidencing the surrendered Warrants are received by the Company at its principal
offices.

         (d) Upon the  surrender  of  Warrant  certificates  and  payment of the
Exercise  Payment  (in cash,  except in the event of a cashless  exercise),  the
Company,  at its  expense,  shall  issue  and  cause  to be  delivered  with all
reasonable  dispatch,  and in any event within ten (10) days thereafter,  to the
Warrantholder  a certificate  or  certificates  for the number of full Shares so
acquired upon the exercise of the Warrant,  together with cash in respect of any
fractional  Shares  otherwise  issuable  upon  such  surrender,   determined  in
accordance  with Section 7 hereof.  Such  certificate or  certificates  shall be
deemed to have been issued, and the Warrantholder shall be deemed to have become
a holder of record of such  Shares,  as of the date of surrender of the

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<PAGE>

Warrants being exercised and (in the case of exercise  pursuant to Section 2(a))
payment  of  the  Exercise  Payment  notwithstanding  that  the  certificate  or
certificates representing such securities shall not actually have been delivered
or that the stock  transfer  books of the  Company  shall  then be  closed.  The
Warrants  shall be exercisable  at the election of the  Warrantholder  either in
full  or  from  time  to time in  part  and,  in the  event  that a  certificate
evidencing  Warrants  is  exercised  in  respect of fewer than all of the Shares
specified  therein at any time prior to the Termination  Date, a new certificate
evidencing the remaining portion of the Warrants shall be issued by the Company.

         Section 3.  Payment of Taxes.  The Company  will pay all  transfer  and
stamp  taxes and fees,  if any,  attributable  to the  initial  issuance  of the
Warrants or the issuance of Shares upon exercise of the Warrants.

         Section 4. Mutilated or Missing  Warrants.  In case the  certificate or
certificates  evidencing  any  Warrants  shall be  mutilated,  lost,  stolen  or
destroyed,  the Company  shall,  at the request of the  affected  Warrantholder,
issue and deliver in exchange and substitution for and upon  cancellation of the
mutilated  certificate or  certificates,  or in lieu of and substitution for the
certificate or certificates lost, stolen or destroyed, a new Warrant certificate
or certificates of like tenor and  representing an equivalent right or interest,
but only upon receipt of evidence reasonably  satisfactory to the Company of the
loss, theft, destruction or mutilation of such Warrant and, if requested, at the
cost  and  expense  of  the  Warrantholder  (in  the  case  of  loss,  theft  or
destruction),  an  unsecured  bond of  indemnity  in form and amount  reasonably
satisfactory to the Company.  Such  substitute  Warrant  certificate  shall also
comply with such other reasonable regulations as the Company may prescribe.

         Section 5. Reservation of Common Shares.  There has been reserved,  and
the  Company  shall at all times  keep  reserved  and  available  so long as any
Warrants remain outstanding, out of its authorized share capital, such number of
Shares as shall be subject to purchase  under all  outstanding  Warrants.  Every
transfer  agent for the  Common  Shares  and  other  securities  of the  Company
issuable  upon the  exercise  of Warrants  will be  irrevocably  authorized  and
directed at all times to reserve  such number of  authorized  Common  Shares and
other securities as shall be requisite for such purposes.  The Company will keep
a copy of this  Agreement  on file with  every  transfer  agent  for the  Common
Shares.  The Company will supply every such  transfer  agent with duly  executed
stock and other certificates,  as appropriate, for

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<PAGE>

such purpose and will provide or otherwise  make available any cash which may be
payable as provided in Section 7 hereof.

         Section 6. Adjustment of Number and Kind of Securities.  The number and
kind of securities purchasable upon the exercise of the Warrants and the Warrant
Price shall be subject to  adjustment  from time to time upon the  happening  of
certain events, as follows:

         6.1.  Anti-Dilution  Provisions  And  Other  Adjustments.  In  order to
prevent  dilution of the rights  granted  hereunder,  the Warrant Price shall be
subject to adjustment  from time to time in accordance with this Section 6. Upon
each   adjustment  of  the  Warrant  Price  pursuant  to  this  Section  6,  the
Warrantholder  shall  thereafter  be entitled to acquire upon  exercise,  at the
Warrant Price resulting from such adjustment, the number of Shares obtainable by
multiplying the Warrant Price in effect  immediately prior to such adjustment by
the  number  of  Shares  acquirable  immediately  prior to such  adjustment  and
dividing  the  product   thereof  by  the  Warrant  Price  resulting  from  such
adjustment.

              (a)  Adjustment  for Issue or Sale of  Common  Shares at Less than
Specified  Prices.  Except as  provided  in  Sections  6.3 or 6.5 below,  if and
whenever on or after the date hereof the Company  shall issue or sell,  or shall
in accordance with subparagraphs  6.1(a)(1) to (8), inclusive, be deemed to have
issued or sold (such issuance or sale,  whether actual or deemed,  a "Triggering
Transaction") any Common Shares for a consideration per share less than

              (I) (if the  Common  Shares  are not  traded on the New York Stock
         Exchange,  the American Stock Exchange or the Nasdaq  National  Market)
         U.S.  $6.75 then  forthwith  upon such issue or sale the Warrant  Price
         shall,  subject to subparagraphs  (1) to (8) of this Section 6.1(a), be
         reduced to the Warrant  Price  (calculated  to the  nearest  tenth of a
         cent) determined by dividing: (i) an amount equal to the sum of (x) the
         product  derived  by  multiplying  the Number of Common  Shares  Deemed
         Outstanding  immediately  prior to such  Triggering  Transaction by the
         Warrant  Price  then in  effect,  plus (y) the  consideration,  if any,
         received  by  the  Company  upon   consummation   of  such   Triggering
         Transaction,  by (ii) an amount  equal to the sum of (x) the  Number of
         Common Shares Deemed  Outstanding  immediately prior to such Triggering
         Transaction  plus (y) the number of shares of Common  Stock  issued (or
         deemed to be issued in accordance with subparagraphs  6.1(a)(1) to (8))
         in connection with the Triggering Transaction; or

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<PAGE>

              (II) (if the  Common  Shares  are  traded  on the New  York  Stock
         Exchange,  the American Stock Exchange or the Nasdaq  National  Market)
         the average Market Price for the ten trading days immediately preceding
         such issuance or sale, then forthwith upon such Triggering Transaction,
         the Warrant Price shall,  subject to  subparagraphs  (1) to (8) of this
         Section  6.1(a),  be reduced to the Warrant  Price  (calculated  to the
         nearest tenth of a cent) determined by multiplying the Warrant Price in
         effect immediately prior to the time of such Triggering  Transaction by
         a fraction,  the  numerator of which shall be the sum of (x) the Number
         of  Common  Shares  Deemed   Outstanding   immediately  prior  to  such
         Triggering  Transaction  and (y) the number of Common  Shares which the
         aggregate  consideration  received by the Company upon such  Triggering
         Transaction  would  purchase  at the average  Market  Price for the ten
         trading days immediately preceding such Triggering Transaction, and the
         denominator  of which  shall be the  Number  of  Common  Shares  Deemed
         Outstanding immediately after such Triggering Transaction.

         For  purposes  of this  Section 6, the term  "Number  of Common  Shares
Deemed  Outstanding"  at any given  time shall mean the sum of (i) the number of
Common  Shares  outstanding  at such time,  and (ii) the number of Common Shares
deemed to be outstanding under  subparagraphs  6.1(a)(1) to (8),  inclusive,  at
such time.

         For  purposes of  determining  the  adjusted  Warrant  Price under this
Section  6.1(a),  the  following  subsections  (1) to (8),  inclusive,  shall be
applicable:

              (1) In case the  Company  at any time  shall in any  manner  grant
         (whether directly or by assumption in an amalgamation or otherwise) any
         rights to subscribe for or to purchase, or any options for the purchase
         of, Common Shares or any stock or other securities  convertible into or
         exchangeable  for Common  Shares (such  rights or options  being herein
         called  "Options"  and  such  convertible  or  exchangeable   stock  or
         securities being herein called  "Convertible  Securities"),  whether or
         not  such  Options  or the  right  to  convert  or  exchange  any  such
         Convertible Securities are immediately  exercisable,  and the price per
         share  for  which  the  Common  Shares  are  issuable  upon   exercise,
         conversion or exchange (determined by dividing (x) the total amount, if
         any,  received or  receivable by the Company as  consideration  for the
         granting  of  such  Options,  plus  the  minimum  aggregate  amount  of
         additional  consideration  payable to the Company  upon the exercise of
         all such  Options,  plus,  in the case of such Options  which relate to
         Convertible  Securities,  the

                                      -10-
<PAGE>

         minimum aggregate amount of additional  consideration,  if any, payable
         upon the  issue  or sale of such  Convertible  Securities  and upon the
         conversion  or exchange  thereof,  by (y) the total  maximum  number of
         Common  Shares  issuable  upon  the  exercise  of such  Options  or the
         conversion or exchange of such  Convertible  Securities)  shall be less
         than the  average  Market  Price in  effect  for the ten  trading  days
         immediately  prior to the time of the  granting  of such Option (if the
         Common Shares are traded on The New York Stock  Exchange,  The American
         Stock  Exchange or The National  Nasdaq  Market) or U.S.  $6.75 (if the
         Common  Shares  are not  traded  on The New York  Stock  Exchange,  The
         American Stock Exchange,  or the Nasdaq National Market) then the total
         maximum  amount of Common  Shares  issuable  upon the  exercise of such
         Options,  or, in the case of Options for Convertible  Securities,  upon
         the conversion or exchange of such Convertible Securities, shall (as of
         the date of granting of such Options) be deemed to be  outstanding  and
         to have been  issued and sold by the  Company for such price per share.
         No  adjustment of the Warrant Price shall be made upon the actual issue
         of such Common Shares or such Convertible  Securities upon the exercise
         of such  Options,  except as  otherwise  provided in  subparagraph  (3)
         below.

              (2) In case the  Company  at any time  shall in any  manner  issue
         (whether  directly or by assumption in an amalgamation or otherwise) or
         sell any Convertible Securities,  whether or not the rights to exchange
         or convert  thereunder are immediately  exercisable,  and the price per
         share for which Common  Shares are  issuable  upon such  conversion  or
         exchange  (determined  by  dividing  (x) the total  amount  received or
         receivable  by the  Company as  consideration  for the issue or sale of
         such  Convertible  Securities,  plus the  minimum  aggregate  amount of
         additional  consideration,  if any,  payable  to the  Company  upon the
         conversion  or exchange  thereof,  by (y) the total  maximum  number of
         Common  Shares  issuable  upon the  conversion  or exchange of all such
         Convertible  Securities) shall be less than the average Market Price in
         effect for the ten trading days  immediately  prior to the time of such
         issue or sale (if the  Common  Shares  are traded on The New York Stock
         Exchange,  The American Stock Exchange,  or The Nasdaq National Market)
         or U.S.  $6.75 (if the  Common  Shares  are not  traded on The New York
         Stock  Exchange,  The American Stock  Exchange,  or The Nasdaq National
         Market),  then the total maximum number of Common Shares  issuable upon
         conversion or exchange of all such Convertible  Securities shall (as of
         the date of the

                                      -11-
<PAGE>

         issue  or  sale  of  such  Convertible  Securities)  be  deemed  to  be
         outstanding  and to have been  issued and sold by the  Company for such
         price per share.  No adjustment of the Warrant Price shall be made upon
         the actual issue of such Common  Shares upon  exercise of the rights to
         exchange  or  convert  under  such  Convertible  Securities,  except as
         otherwise provided in subparagraph (3) below.

              (3) If the purchase price provided for in any Options  referred to
         in subparagraph (1), the additional consideration, if any, payable upon
         the conversion or exchange of any Convertible Securities referred to in
         subparagraphs  (1) or  (2),  or  the  rate  at  which  any  Convertible
         Securities  referred to in subparagraph (1) or (2) are convertible into
         or exchangeable  for Common Shares shall change at any time (other than
         under or by reason of provisions  designed to protect against  dilution
         of the type set forth in Section 6.1 (a) or (b)),  the Warrant Price in
         effect at the time of such change shall  forthwith be readjusted to the
         Warrant  Price  which  would  have been in effect at such time had such
         Options or Convertible  Securities still outstanding  provided for such
         changed purchase price, additional consideration or conversion rate, as
         the case may be, at the time initially granted,  issued or sold. If the
         purchase price provided for in any Option  referred to in  subparagraph
         (1) or the rate at which  any  Convertible  Securities  referred  to in
         subparagraphs  (1) or (2)  are  convertible  into or  exchangeable  for
         Common  Shares,  shall be  reduced  at any time  under or by  reason of
         provisions with respect thereto  designed to protect against  dilution,
         then in case of the delivery of Common  Shares upon the exercise of any
         such Option or upon  conversion  or  exchange  of any such  Convertible
         Security, the Warrant Price then in effect hereunder shall forthwith be
         adjusted to such respective amount as would have been obtained had such
         Option or  Convertible  Security  never been  issued as to such  Common
         Shares and had  adjustments  been made upon the  issuance of the Common
         Shares  delivered  as  aforesaid,  but  only  if as a  result  of  such
         adjustment  the  Warrant  Price  then in  effect  hereunder  is  hereby
         reduced.

              (4) On the  expiration  of any  Option or the  termination  of any
         right to convert or exchange any  Convertible  Securities,  the Warrant
         Price then in effect  hereunder  shall  forthwith  be  increased to the
         Warrant  Price  which  would  have  been in  effect at the time of such
         expiration or termination had such Option or Convertible Securities, to
         the  extent

                                      -12-
<PAGE>

         outstanding immediately prior to such expiration or termination,  never
         been issued.

              (5) In case any  Options  shall be issued in  connection  with the
         issue or sale of other securities of the Company,  together  comprising
         one  integral  transaction  in  which  no  specific   consideration  is
         allocated to such Options by the parties thereto, such Options shall be
         deemed to have been issued without consideration.

              (6) In case any Common Shares,  Options or Convertible  Securities
         shall be issued or sold or deemed to have been issued or sold for cash,
         the  consideration  received  therefor shall be deemed to be the amount
         received by the Company therefor. In case any Common Shares, Options or
         Convertible  Securities  shall be  issued  or sold for a  consideration
         other  than  cash,  the  amount of the  consideration  other  than cash
         received by the Company  shall be the fair value of such  consideration
         as  determined  in good faith by the Board of Directors of the Company.
         In case any Common Shares,  Options or Convertible  Securities shall be
         issued in connection  with any  amalgamation in which the Company is an
         amalgamating corporation, the amount of consideration therefor shall be
         deemed  to be the fair  value of such  portion  of the net  assets  and
         business of the other  corporation which is a party to the amalgamation
         as shall be attributed by the Board of Directors of the Company in good
         faith to such Common Shares, Options or Convertible Securities,  as the
         case may be.

              (7) In case the Company shall declare a dividend or make any other
         distribution  upon the  stock of the  Company  payable  in  Options  or
         Convertible  Securities,  then in such case any Options or  Convertible
         Securities, as the case may be, issuable in payment of such dividend or
         distribution  shall be  deemed  to have  been  issued  or sold  without
         consideration.

              (8) For purposes of this Section 6.1(a), in case the Company shall
         take a record of the  holders of its Common  Shares for the  purpose of
         entitling them (x) to receive a dividend or other distribution  payable
         in Common  Shares,  Options  or in  Convertible  Securities,  or (y) to
         subscribe  for  or  purchase  Common  Shares,  Options  or  Convertible
         Securities, then such record date shall be deemed to be the date of the
         issue or sale of the Common  Shares  deemed to have been issued or sold
         upon the  declaration  of such  dividend  or the  making of such  other
         distribution  or the

                                      -13-
<PAGE>

         date of the granting of such right or subscription or purchase,  as the
         case may be.

              (b) In case the Company  shall (i) pay a dividend in Common Shares
or make a distribution in Common Shares or (ii) subdivide its outstanding Common
Shares,  the Warrant Price in effect  immediately  prior to such  subdivision or
dividend shall be  proportionately  reduced by the same ratio as the dividend or
subdivision.  In case the  Company  shall at any time  combine  its  outstanding
Common Shares, the Warrant Price in effect immediately prior to such combination
shall be  proportionately  increased by the same ratio as the  combination.  Any
adjustment  made  pursuant to this  subsection  6.1 (b) shall  become  effective
immediately on the effective date of such event  retroactive to the record date,
if any, for such event.

              (c)  Whenever  the number of Common  Shares  purchasable  upon the
exercise of Warrants is adjusted as herein provided,  the Company shall cause to
be promptly  delivered  to the  Warrantholder  notice of such  adjustment  and a
certificate  of the chief  financial  officer of the Company  setting  forth the
number of Common Shares purchasable upon the exercise of the Warrants after such
adjustment,  the Warrant Price that will be effective after such  adjustment,  a
brief  statement of the facts  requiring such  adjustment and the computation by
which  such  adjustment  was  made.  If such  notice  relates  to an  adjustment
resulting  from an event referred to in Section 8, such notice shall be included
as  part  of the  notice  required  to be  delivered  and  published  under  the
provisions of Section 8 hereof.

         6.2. No Adjustment for Dividends. Except as provided in this Section 6,
no adjustment  to the Warrants or any provision or condition  thereof in respect
of any dividends or distributions  out of earnings shall be made during the term
of the Warrants or upon the exercise of Warrants.

         6.3. Dividends Not Paid Out of Earnings or Earned Surplus. In the event
the  Company  shall  declare a dividend  upon the Common  Shares  (other  than a
dividend  payable in Common  Shares)  payable  otherwise than out of earnings or
earned  surplus,  determined in accordance  with generally  accepted  accounting
principles,   including  the  making  of  appropriate  deductions  for  minority
interests,   if  any,  in  subsidiaries  (herein  referred  to  as  "Liquidating
Dividends"),  then, as soon as possible after the exercise of this Warrant,  the
Company shall pay to the person  exercising  such Warrant an amount equal to the
aggregate  value  at the  time of such  exercise  of all  Liquidating  Dividends
(including  but not limited to the Common Shares which would have been issued

                                      -14-
<PAGE>

at the time of such earlier  exercise and all other  securities which would have
been issued with respect to such Common Shares by reason of stock splits,  stock
dividends,  amalgamations or reorganizations,  or for any other reason). For the
purposes  of this  subsection  6.3,  a  dividend  other  than in cash  shall  be
considered  payable out of earnings  or earned  surplus  only to the extent that
such earnings or earned surplus are charged an amount equal to the fair value of
such  dividend  as  determined  in good faith by the Board of  Directors  of the
Company.

         6.4. Reclassification, Amalgamation, etc. If any capital reorganization
or  reclassification of the share capital of the Company, or amalgamation of the
Company with another corporation, or the sale of all or substantially all of its
assets to another  corporation  shall be effected in such a way that  holders of
Common  Shares  shall be entitled to receive  stock,  securities,  cash or other
property with respect to or in exchange for Common Shares,  then, as a condition
of such  reorganization,  reclassification,  amalgamation  or sale,  lawful  and
adequate provision shall be made whereby the Warrantholder  shall have the right
to acquire  and receive  upon  exercise  of this  Warrant  such shares of stock,
securities,  cash  or  other  property  issuable  or  payable  (as  part  of the
reorganization,  reclassification,  amalgamation  or sale) with respect to or in
exchange for such number of outstanding  Shares as would have been received upon
exercise of this Warrant at the Warrant  Price then in effect.  The Company will
not effect  any such  amalgamation  or sale,  unless  prior to the  consummation
thereof the amalgamated  corporation or the  corporation  purchasing such assets
shall assume by written  instrument mailed or delivered to the Warrantholder the
obligation to deliver to such holder such shares of stock,  securities or assets
as, in accordance with the foregoing provisions,  such holder may be entitled to
purchase. If a purchase, tender or exchange offer is made to and accepted by the
holders of more than 50% of the  outstanding  Common Shares of the Company,  the
Company  shall not effect any  amalgamation  or sale with the person having made
such  offer  or  with  any  Affiliate  of  such  person,  unless  prior  to  the
consummation  of such  amalgamation  or sale the  Warrantholder  shall have been
given a  reasonable  opportunity  to then elect to receive  upon the exercise of
this Warrant  either the stock,  securities or assets then issuable with respect
to the Common Shares of the Company or the stock,  securities or assets,  or the
equivalent,  issued to previous  holders of the Common Shares in accordance with
such offer.  For purposes hereof the term  "Affiliate" with respect to any given
person shall mean any person controlling,  controlled by or under common control
with  the  given  person.  In  the  event  of  a

                                      -15-
<PAGE>

merger  described in Section  368(a)(2)(E) of the Internal  Revenue Code of 1986
(or any successor provision), in which the Company is the surviving corporation,
the right to purchase  Shares upon exercise of the Warrants  shall  terminate on
the date of such merger and thereupon  the Warrants  shall become null and void,
but only if the  controlling  corporation  (after  such  event)  shall  agree to
substitute for the Warrants its warrants entitling the Warrantholder to purchase
the kind and amount of shares and other  securities  and property which it would
have been entitled to receive had the Warrants been exercised  immediately prior
to such merger.  Any such  agreements  referred to in this  subsection 6.3 shall
provide  for  adjustments,  which  shall  be as  nearly  equivalent  as  may  be
practicable to the adjustments provided for in this Section 6, and shall contain
substantially the same terms,  conditions and provisions as are contained herein
immediately  prior to such event.  The  provisions of this  subsection 6.4 shall
similarly apply to successive amalgamations, sales or conveyances.

         6.5. No Adjustment for Exercise of Certain Options,  Warrants, Etc. The
provisions  of this  Section  6 shall  not apply to any  Common  Shares  issued,
issuable or deemed outstanding under  subparagraphs  6.1(a)(1) to (8) inclusive:
(i) to any person  pursuant to any stock option,  stock purchase or similar plan
or  arrangement  for the benefit of employees,  consultants  or directors of the
Company or its subsidiaries in effect on the date hereof or hereafter adopted by
the Board of Directors of the Company, or (ii) pursuant to options, warrants and
conversion  rights in existence on the date hereof,  including  the  Convertible
Shares.

         6.6. Grant Issue or Sale of Options, Convertible Securities, or Rights.
If at any time or from time to time on or after the date of this Agreement,  the
Company shall grant, issue or sell any Options, Convertible Securities or rights
to purchase  property (the "Purchase  Rights") pro rata to the record holders of
any class of share capital of the Company and such grants, issuances or sales do
not result in an adjustment of the Warrant  Price under Section  6.1(a)  hereof,
then the  Warrantholder  shall be entitled to acquire  (within  thirty (30) days
after the later to occur of the initial exercise date of such Purchase Rights or
receipt by the Warrantholder of the notice  concerning  Purchase Rights to which
the  Warrantholder  shall be  entitled  under  Section  8) and  upon  the  terms
applicable to such Purchase Rights either:

              (a) the aggregate  Purchase Rights which the  Warrantholder  could
         have  acquired  if it had held the  number  of Shares  acquirable  upon
         exercise of this Warrant

                                      -16-
<PAGE>

         immediately  before the grant issuance or sale of such Purchase Rights;
         provided  that  if  any  Purchase   Rights  were   distributed  to  the
         Warrantholder  of Common  Shares  without  the  payment  of  additional
         consideration by such holders,  corresponding  Purchase Rights shall be
         distributed to the  Warrantholder as soon as possible after exercise of
         this  Warrant  and it  shall  not be  necessary  for the  Warrantholder
         specifically to request delivery of such rights; or

              (b) in the event that any such Purchase  Rights shall have expired
         or shall  expire  prior to the end of said thirty (30) day period,  the
         number of Shares or the  amount  of  property  which the  Warrantholder
         could have  acquired  upon such  exercise at the time or times at which
         the Company granted, issued or sold such expired Purchase Rights.

         6.7.  Nominal  Value of Common  Shares.  Before taking any action which
would cause an adjustment  effectively reducing the portion of the Warrant Price
allocable to each Share below the then  nominal  value per Share  issuable  upon
exercise of the Warrants,  the Company will take any corporate action which may,
in the  opinion of its  counsel,  be  necessary  in order that the  Company  may
validly and legally issue fully paid and  nonassessable  Shares upon exercise of
the Warrants.

         6.8.  Independent Public Accountants.  The Company may retain a firm of
independent  public  accountants of recognized  national  standing in the United
States  (which may be any such firm  regularly  employed by the Company) to make
any computation required under this Section.

         6.9. Statement on Warrant Certificates. Irrespective of any adjustments
in the  number  of  securities  issuable  upon  exercise  of  Warrants,  Warrant
certificates  theretofore or thereafter  issued may continue to express the same
number of securities as are stated in the similar Warrant certificates initially
issuable  pursuant to this Agreement.  However,  the Company may, at any time in
its reasonable  discretion,  make any change in the form of Warrant  certificate
that it may deem appropriate and that does not affect the substance thereof; and
any Warrant certificate hereafter issued,  whether upon registration of transfer
of, or in exchange or substitution for, an outstanding Warrant certificate,  may
be in the form so changed.

         6.10.  Adjustment  by Board of  Directors.  If any  event  occurs as to
which,  in the opinion of the Board of Directors of the Company,  the provisions
of this Section 6 are not strictly

                                      -17-
<PAGE>

applicable or if strictly  applicable would not fairly protect the rights of the
Warrantholder  in accordance  with the essential  intent and  principles of such
provisions,  then  the  Board  of  Directors  shall  make an  adjustment  in the
application of such  provisions,  in accordance  with such essential  intent and
principles, so as to protect such rights as aforesaid, but in no event shall any
adjustment  have the  effect  of  increasing  the  Warrant  Price  as  otherwise
determined  pursuant to any of the  provisions  of this  Section 6 except in the
case of a combination  of shares of a type  contemplated  in Section  6.1(a) and
then in no event to an amount larger than the Warrant Price as adjusted pursuant
to Section 6.1(a).

         Section 7. Fractional Interests. The Company shall not issue fractional
Common  Shares upon any  exercise of any  Warrants.  If any fraction of a Common
Share  would,  except for the  provisions  of this Section 7, be issuable on the
exercise of any  Warrants,  the Company shall pay an amount in cash equal to the
Market Price (as defined in Section 2(b) hereof, except if the Common Shares are
not publicly  traded,  as  determined in good faith by the Board of Directors of
the Company)  multiplied by such  fraction,  provided,  however,  that no amount
shall be paid by the Company of less than U.S. $5.00.

         Section 8. No Rights as Shareholder, Notices to Warrantholder.  Nothing
contained in this  Agreement or in the Warrants shall be construed as conferring
upon the  Warrantholder  any rights as a shareholder  of the Company,  including
(without  limitation) the right to vote, receive  dividends,  consent or receive
notices  as a  shareholder  in respect of any  meeting of  shareholders  for the
election of  directors  of the Company or any other  matter,  except as provided
herein.  If,  however,  at any time prior to the  expiration of the Warrants and
prior to their exercise in full,  any one or more of the following  events shall
occur:

              (a) any action  which  would  require an  adjustment  pursuant  to
         Section 6.1 or 6.3; or

              (b) the Company  shall  declare any cash  dividend upon its Common
         Shares; or

              (c) the Company  shall declare any dividend upon its Common Shares
         payable in stock or make any special dividend or other  distribution to
         the holders of its Common Shares; or

                                      -18-
<PAGE>

              (d) the Company shall offer Purchase  Rights to the holders of its
         Common Shares; or

              (e) there shall be any capital  reorganization or reclassification
         of the share  capital of the  Company,  including  any  subdivision  or
         combination of its  outstanding  Common Shares,  or amalgamation of the
         Company  with,  or sale of all or  substantially  all of its assets to,
         another corporation; or

              (f) there shall be a dissolution, liquidation or winding up of the
         Company (other than in connection  with an  amalgamation or sale of its
         property,  assets and  business as an entirety or  substantially  as an
         entirety);

then  the   Company   shall  give  notice  in  writing  of  such  event  to  the
Warrantholder,  as provided in Section 10 hereof,  at least 20 days prior to (i)
the date fixed as a record  date or the date of closing the  transfer  books for
the  determination  of  the  shareholders  entitled  to any  relevant  dividend,
distribution,  Purchase  Rights  or other  rights  or for the  determination  of
shareholders entitled to vote on such proposed reorganization, reclassification,
amalgamation,  sale,  dissolution,  liquidation  or winding up and (ii) the date
when any such reorganization, reclassification, amalgamation, sale, dissolution,
liquidation or winding up shall take place.  Such notice in accordance  with the
foregoing  clause  (i) shall  also  specify,  in the case of any such  dividend,
distribution or Purchase Rights,  the date on which the holders of Common Shares
shall be entitled  thereto,  and such notice in  accordance  with the  foregoing
clause (ii) shall also  specify  the date on which the holders of Common  Shares
shall be  entitled to  exchange  their  Common  Shares for  securities  or other
property deliverable upon such reorganization,  reclassification,  amalgamation,
sale, dissolution, liquidation or winding up, as the case may be.

         Section  9. No  Dilution  or  Impairment.  The  Company  will  not,  by
amendment of its charter or through reorganization,  amalgamation,  dissolution,
sale of  assets  or any  other  voluntary  action,  avoid or seek to  avoid  the
observance or performance  of any of the terms of this Warrant,  but will at all
times in good  faith  assist in the  carrying  out of all such  terms and in the
taking of all such action as may be necessary or appropriate in order to protect
the rights of the Warrantholder  against dilution or other  impairment.  Without
limiting the generality of the foregoing,  the Company will not increase the par
value of any shares  receivable  upon the  exercise  of this  Warrant  above the
amount payable therefor upon such exercise,  and at all times will

                                      -19-
<PAGE>

take all such  action  as may be  necessary  or  appropriate  in order  that the
Company may validly and legally issue fully paid and non-assessable  shares upon
the exercise of this Warrant.

         Section 10. Notices. Any notice hereunder shall be in writing and shall
be effective  when  delivered in person or by facsimile  transmission,  or seven
business  days after being  mailed by  certified  or  registered  mail,  postage
prepaid,  return receipt  requested,  to the appropriate  party at the following
addresses:

If to the Warrantholder:

                  Warburg Pincus Ventures, L.P.
                  466 Lexington Avenue
                  New York, New York 10017-3147
                  Facsimile: 212-878-9351
                  Attention: Mr. Joel Ackerman

with a copy to:

                  Willkie Farr & Gallagher
                  787 Seventh Avenue
                  New York, New York 10019
                  Facsimile: 212-728-8111
                  Attention: Steven J. Gartner, Esq.

If to the Company:

                  Sonus Corp.
                  111 SW Fifth Avenue, Suite 1620
                  Portland, Oregon 97204
                  Facsimile: 503-225-9309
                  Attention: Mr. Brandon M. Dawson

with copy to:

                  Sonus Corp.
                  111 SW Fifth Avenue, Suite 1620
                  Portland, Oregon 97204
                  Facsimile: 503-225-9309
                  Attention:  Brian Thompson, Esq.

or, in each case, to such other address as the parties may hereinafter designate
by like notice.

         Section  11.  Successors.  All the  covenants  and  provisions  of this
Agreement  for the benefit of the  Warrantholder  or the Company  shall bind and
inure to the benefit of their successors

                                      -20-
<PAGE>

and, in the case of the Warrantholder,  permitted assigns.  This Agreement shall
not be assignable by the Company.

         Section  12.  Amalgamation  of  the  Company.  The  Company  shall  not
amalgamate with any other  corporation or sell all or  substantially  all of its
property  to another  corporation,  unless  the  provisions  of Section  6.4 are
complied with.

         Section 13. Remedies.  The Company  stipulates that the remedies at law
of the  Warrantholder  in  the  event  of any  default  by  the  Company  in the
performance  of or compliance  with any of the terms of this Warrant are not and
will not be adequate, and that the same may be specifically enforced.

         Section 14.  Subdivisions  of Rights.  The Warrants (as well as any new
warrants  issued  pursuant to the provisions of this Section) are  exchangeable,
upon the surrender  hereof by the  Warrantholder  at the principal office of the
Company for any number of new  warrants of like tenor and date  representing  in
the aggregate the right to subscribe for and purchase the number of Shares which
may be subscribed for and purchased hereunder.

         Section 15. Applicable Law, Submission to Jurisdiction.  This Agreement
shall be deemed to be a  contract  made  under the laws of the State of New York
and for all purposes shall be construed in accordance  with the internal laws of
said State (without reference to its rules as to conflicts of laws). The Company
hereby agrees to the  non-exclusive  jurisdiction  of the courts of the State of
New York or the  federal  courts  sitting in the City of New York in  connection
with any action arising out of this Agreement.

         Section 16. Benefits of this  Agreement.  Except as provided in Section
1.2 and Section 11, nothing in this Agreement  shall be construed to give to any
person or corporation  other than the Company and the Warrantholder any legal or
equitable  right,  remedy or claim under this  Agreement.  Except as provided in
Section 1.2 and Section 11, this  Agreement  shall be for the sole and exclusive
benefit of the Company and the Warrantholder.

                                      -21-
<PAGE>


         IN WITNESS  WHEREOF,  the parties have caused this Agreement to be duly
executed, all as of the date and year first above written.

                                SONUS CORP.


                                By: /s/ Brandon M. Dawson
                                   Name: Brandon M. Dawson
                                   Title:  Chairman and Chief Executive Officer


                                WARBURG, PINCUS VENTURES, L.P.

                                By: Warburg, Pincus & Co.,
                                    General Partner


                                By: Authorized Signature
                                    Name:
                                    Title:


                                      -22-
<PAGE>

                                                                       EXHIBIT 1


                          [FORM OF WARRANT CERTIFICATE]

         "THE WARRANTS  REPRESENTED BY THIS  CERTIFICATE,  AND THE COMMON SHARES
         ISSUABLE UPON EXERCISE OF SUCH WARRANTS, HAVE NOT BEEN REGISTERED UNDER
         THE UNITED STATES  SECURITIES ACT OF 1933 OR THE SECURITIES LAWS OF ANY
         STATE OF THE UNITED STATES OR ANY PROVINCE OF CANADA. SUCH WARRANTS MAY
         NOT  BE  SOLD,  OFFERED  FOR  SALE,  ASSIGNED,  EXCHANGED,  PLEDGED  OR
         HYPOTHECATED OR OTHERWISE  TRANSFERRED,  IN ANY MANNER, AND SUCH COMMON
         SHARES MAY NOT BE OFFERED FOR SALE,  SOLD,  PLEDGED OR  HYPOTHECATED OR
         TRANSFERRED  IN THE  ABSENCE  OF SUCH  REGISTRATION  OR AN  OPINION  OF
         COUNSEL, REASONABLY SATISFACTORY TO THE COMPANY, THAT AN EXEMPTION FROM
         SUCH  REGISTRATION  IS  AVAILABLE."  THE WARRANTS  REPRESENTED  BY THIS
         CERTIFICATE MAY NOT BE TRADED IN CANADA EXCEPT AS PERMITTED BY RELEVANT
         CANADIAN SECURITIES LAWS.


                                                            AMENDED AND RESTATED
                                                     WARRANT CERTIFICATE NO. W-1


                                   SONUS CORP.

                            (ORGANIZED UNDER THE LAWS
                               OF YUKON TERRITORY)

                                                                 October 1, 1999


                       WARRANTS TO PURCHASE COMMON SHARES


         This certifies that, for value received, Warburg, Pincus Ventures, L.P.
(the  "Warrantholder")  is the  registered  owner  of  2,000,000  warrants  (the
"Warrants") each to purchase from Sonus Corp. (the "Company"), at any time prior
to 5:00 p.m., Pacific Time, on October 1, 2004, one common share of the Company,
without par value (a "Common  Share") at a purchase  price per Common Share (the
"Warrant Price"),  equal to U.S. $6.75,  provided that if the Series A Amendment
Filing Date has not occurred on or prior to March 31, 2000,  then from and after
March 31,  2000,  the Warrant  Price shall equal U.S.  $4.00.  The  Warrants are
subject
                                      -1-
<PAGE>

to, and the Warrantholder,  by acceptance of this certificate,  consents to, all
the terms and provisions of, the Amended and Restated Warrant Agreement dated as
of October 1, 1999,  between the  Warrantholder  and the Company  (the  "Warrant
Agreement"). Any capitalized terms used herein and not defined herein shall have
the meanings assigned to such terms in the Warrant Agreement.

         The Warrants  evidenced  hereby may be exercised in whole or in part by
presentation  of this Warrant  Certificate  with the  Purchase  Form herein duly
executed  (with a signature  guarantee as provided  therein),  and  simultaneous
payment of the Warrant Price for each Warrant exercised, at the principal office
of the  Company.  Payment  of such  price  shall  be made at the  option  of the
Warrantholder  in cash by certified or official bank check or by wire  transfer.
Subject  to the  terms and  conditions  set  forth in  Section 2 of the  Warrant
Agreement,  the  Warrantholder  may also receive  Common Shares without any cash
payment by presentation of this Warrant  Certificate with the Cashless  Exercise
Form herein duly executed  (with a signature  guarantee as provided  therein) at
the principal office of the Company.

         Upon any partial exercise of the Warrants evidenced hereby, there shall
be signed and issued to the  Warrantholder a new Warrant  Certificate in respect
of the Common  Shares as to which the Warrants  evidenced  hereby shall not have
been exercised.  These Warrants may be exchanged at the office of the Company by
surrender  of this  Warrant  Certificate  properly  endorsed for one or more new
Warrants of the same aggregate  number of Common Shares as here evidenced by the
Warrant or Warrants  exchanged.  No fractional Common Shares will be issued upon
the exercise of rights to purchase hereunder, but the Company shall pay the cash
value  of any  fraction  otherwise  issuable  upon the  exercise  of one or more
Warrants, as provided in the Warrant Agreement.

         The Warrants  evidenced hereby are transferable only in accordance with
the terms and conditions set forth in Section 1.2 of the Warrant Agreement.

         This Warrant  Certificate does not entitle the  Warrantholder to any of
the rights of a shareholder of the Company.

                                      -2-
<PAGE>


                                     SONUS CORP.


                                     By: /s/ Brandon M. Dawson

                                     Title: Chairman and Chief Executive Officer


ATTEST:

/s/ Brian S. Thompson

Title:  Secretary


Dated: October 1, 1999



<PAGE>

                                                                       EXHIBIT 2


                                  PURCHASE FORM

Sonus Corp.
111 SW Fifth Avenue, Suite 1620
Portland, Oregon 97204

         Pursuant to Section  2(a) of the  Warrant  Agreement,  as amended,  the
undersigned  hereby  irrevocably  elects  to  exercise  the  right  of  purchase
represented by this Warrant Certificate for, and to purchase thereunder,  ------
common  shares  of  the  Company  (the  "Common  Shares"),   and  requests  that
certificates for such Common Shares be issued in the name of:

Warburg, Pincus Ventures, L.P.
466 Lexington Avenue
New York, New York 10017-3147
Taxpayer Identification Number:  -------------------

If this Warrant Certificate is hereby being exercised with respect to fewer than
all the Common Shares specified herein,  please issue a new Warrant  Certificate
for the  unexercised  balance  of the  Warrants,  registered  in the name of the
undersigned Warrantholder as below indicated and delivered to the address stated
below.

Dated:-----------------------

Name of Warrantholder:

Warburg, Pincus Ventures, L.P.
466 Lexington Avenue
New York, New York 10017-3147

         By:      Warburg, Pincus & Co.
                  General Partner


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


<PAGE>

                                                                       EXHIBIT 3

                             CASHLESS EXERCISE FORM

Sonus Corp.
111 SW Fifth Avenue, Suite 1620
Portland, Oregon 97204

         Pursuant to Section  2(b) of the  Warrant  Agreement,  the  undersigned
hereby  irrevocably  elects to exercise  the right  represented  by this Warrant
Certificate for, and to receive thereunder,  without any cash payment,  --------
common shares of the Company (the "Common Shares") as provided for therein,  and
requests that certificates for such Common Shares be issued in the name of:

Warburg, Pincus Ventures, L.P.
466 Lexington Avenue
New York, New York 10017-3147
Taxpayer Identification Number:  ------------------

If this Warrant Certificate is hereby being exercised with respect to fewer than
all the Common Shares specified herein,  please issue a new Warrant  Certificate
for the  unexercised  balance  of the  Warrants,  registered  in the name of the
undersigned Warrantholder as below indicated and delivered to the address stated
below.

Dated:-----------------------

Name of Warrantholder:

Warburg, Pincus Ventures, L.P.
466 Lexington Avenue
New York, New York 10017-3147

         By:    Warburg, Pincus & Co.
                 General Partner


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


<PAGE>


                                                                       EXHIBIT 4

                       FORM OF OPINION OF DAVIS & COMPANY