Document:

<PAGE>   1
                                                                   EXHIBIT 10.21

                              AGREEMENT OF MERGER

     AGREEMENT OF MERGER dated as of May  , 2000 (this "Agreement") among
Quintus Corporation, a corporation duly organized and existing under the laws of
the State of Delaware ("Parent"), Mustang.com Acquisition Corporation, a
corporation duly organized and existing under the laws of the State of Delaware
and a wholly owned subsidiary of Parent ("Merger Sub"), and Mustang.com, Inc., a
wholly owned subsidiary of Parent ("Merger Sub"), and Mustang.com, Inc., a
corporation duly organized and existing under the laws of the State of
California (the "Company").

                              W I T N E S S E T H

     WHEREAS, the boards of directors of Parent, Merger Sub and the Company have
each determined that it is advisable and in the best interests of their
respective shareholders for Merger Sub to merge with and into the Company (the
"Merger") upon the terms and subject to the conditions set forth herein;

     WHEREAS, in furtherance of the Merger, the boards of directors of Parent
and Merger Sub have each approved the Merger in accordance with the General
Corporation Law of the State of Delaware ("Delaware Law") and upon the terms and
subject to the conditions set forth herein, and the board of directors of the
Company has approved the Merger in accordance with the General Corporation Law
of the State of California ("California Law") and upon the terms and subject to
the conditions set forth herein; and

     WHEREAS, in furtherance of the Merger; the holders of the common stock, no
par value ("Company Common Stock"), of the Company have approved the Merger by
the affirmative vote of a majority of the issued and outstanding shares held by
such holders in accordance with California Law and upon the terms and subject to
the conditions set forth herein;

     NOW, THEREFORE, in consideration of the foregoing and the mutual covenants
and agreements herein contained, and intending to be legally bound hereby,
Parent, Merger Sub and the Company hereby agree as follows:

     Section 1. The Merger. At the Effective Time (as defined below), and upon
the terms and subject to the conditions of this Agreement, California Law and
Delaware Law, Merger Sub shall be merged with and into the Company. As a result
of the Merger, the separate corporate existence of Merger Sub shall cease and
the Company shall continue as the surviving corporation of the Merger (the
"Surviving Corporation").

<PAGE>   2

     SECTION 2. Effective Time. The effective time of the Merger ("Effective
Time") shall be upon filing with the Secretary of State of the State of
California and in accordance with Section 1108 of the California Corporations
Code.

     SECTION 3. Effect of the Merger. At the Effective Time, all the property,
rights, privileges, powers and franchises of the Company and Merger Sub shall
vest in the Surviving Corporation, and all debts, liabilities, obligations,
restrictions, disabilities, and duties of each of the Company and Merger Sub
shall become the debts, liabilities, obligations, restrictions, disabilities,
and duties of the Surviving Corporation.

     SECTION 4. Articles of Incorporation. The Articles of Incorporation of the
Company in effect at the Effective Time shall be the Articles of Incorporation
or the Surviving Corporation until amended in accordance with applicable law.

     SECTION 5. Directors and Officers. The directors of Merger Sub immediately
prior to the Effective Time shall be the initial directors of the Surviving
Corporation, each to hold office in accordance with the Articles of
Incorporation and By-Laws of the Surviving Corporation, and the officers of the
Company immediately prior to the Effective Time shall be the initial officers of
the Surviving Corporation, in each case until their respective successors are
duly elected or appointed and qualified.

     SECTION 6. Effect on Capital Stock. At the Effective Time, by virtue of
the Merger and without any action on the part of Merger Sub, the Company or the
holders of any of the securities of the Company:

     (a)  each share of Company Common Stock issued and outstanding immediately
prior to the Effective Time (other than Dissenting Shares (as defined below)
and shares to be canceled pursuant to Section 6(d)) shall be converted into the
right to receive 0.793 shares of common stock of Parent, par value $0.001 per
share ("Parent Common Stock");

     (b)  each option to purchase shares of Company Common Stock (each, a
"Company Stock Option") issued and outstanding at the Effective Time and all
rights in respect thereof shall be assumed by Parent and shall be deemed to
constitute an option to acquire the same number of shares of Parent Common
Stock as the holder of such Company Stock Option would have been entitled to
receive pursuant to the Merger had such holder exercised such Company Stock
Option in full immediately prior to the Effective Time, at a price per share of
Parent Common Stock equal to (i) the aggregate exercise price for the shares of
Company Common Stock otherwise purchasable pursuant to such Company Stock
Option divided by (ii) the aggregate number of shares of Parent Common Stock
deemed purchasable pursuant to such Company Stock Option;

                                       2
<PAGE>   3
     (c)  each outstanding warrant to purchase shares of Company Common Stock
(each a "Company Stock Warrant") shall be adjusted as necessary to provide
that, at the Effective Time, each Company Stock Warrant outstanding immediately
prior to the Effective Time shall be deemed to constitute a warrant to acquire
the same number of shares of Parent Common Stock as the holder of such Company
Stock Warrant would have been entitled to receive pursuant to the Merger had
such holder exercised such Company Stock Warrant in full immediately prior to
the Effective Time, at a price per share of Parent Common Stock equal to (i) the
aggregate exercise price for the shares of Company Common Stock otherwise
purchasable pursuant to such Company Stock Warrant divided by (ii) the aggregate
number of shares of Parent Common Stock deemed purchasable pursuant to such
Company Stock Warrant;

     (d)  each share of Company Common Stock held by Parent or any of its
subsidiaries immediately prior to the Effective Time shall be canceled and no
payment shall be made with respect thereto;

     (e)  each share of common stock of Merger Sub outstanding immediately
prior to the Effective Time shall be converted into and become one share of
common stock of the Surviving Corporation with the same rights, powers and
privileges as the shares so converted and shall constitute the only outstanding
shares of capital stock of the Surviving Corporation; and

     (f)  no fractional shares of Parent Common Stock will be issued in the
Merger. Instead, each holder of Company Common Stock who would otherwise be
entitled to receive a fraction of a share of Parent Common Stock will receive
an amount of cash equal to the product of (i) such fraction, multiplied by (ii)
the closing price for shares of Parent Common Stock as reported on the Nasdaq
National Market for the trading day immediately preceding the Effective Time.

     SECTION 7.  Dissenting Shares.  (a) Notwithstanding any provision of this
Agreement to the contrary, shares of Company Common Stock that are outstanding
immediately prior to the Effective Time and which are held by shareholders who
shall have exercised and perfected appraisal rights for such shares in
accordance with California Law (collectively, the "Dissenting Shares") shall
not be converted into or represent the right to receive the Merger
Consideration. Such shareholders shall be entitled to receive payment of the
appraised value of such shares held by them in accordance with California Law,
except that all Dissenting Shares held by shareholders who shall have failed to
perfect or who effectively shall have withdrawn or lost their rights to
appraisal of such shares shall thereupon be deemed to have been converted into
and to have become exchangeable for, as of the Effective Time, the right to
receive the Merger

                                       3
<PAGE>   4
Consideration, without any interest thereon, upon surrender of the certificate
or certificates that formerly evidenced such shares.

                                       4
<PAGE>   5
     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
executed as of the date first written above by their respective officers
thereunto duly authorized.

                                   QUINTUS CORPORATION

                                   By: /s/ ALAN K. ANDERSON
                                       ----------------------------------
                                      Name: Alan K. Anderson
                                      Title: Chairman and Chief Executive
                                      Officer

                                   By: /s/ SUSAN SALVESEN
                                       ----------------------------------
                                      Name: Susan Salvesen
                                      Title: Chief Financial Officer & Secretary

                                   MUSTANG.COM ACQUISITION CORPORATION

                                   By: /s/ ALAN K. ANDERSON
                                       ----------------------------------
                                      Name: Alan K. Anderson
                                      Title: President

                                   By: /s/ SUSAN SALVESEN
                                       ----------------------------------
                                      Name: Susan Salvesen
                                      Title: Secretary

                                   MUSTANG.COM, INC.

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

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

                                       5
<PAGE>   6
     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
executed as of the date first written above by their respective officers
thereunto duly authorized.

                                   QUINTUS CORPORATION

                                   By:
                                       ----------------------------------
                                      Name: Alan K. Anderson
                                      Title: Chairman and Chief Executive
                                      Officer

                                   By:
                                       ----------------------------------
                                      Name: Susan Salvesen
                                      Title: Chief Financial Officer & Secretary

                                   MUSTANG.COM ACQUISITION CORPORATION

                                   By:
                                       ----------------------------------
                                      Name: Alan K. Anderson
                                      Title: President

                                   By:
                                       ----------------------------------
                                      Name: Susan Salvesen
                                      Title: Secretary

                                   MUSTANG.COM, INC.

                                   By: /s/ JAMES A. HARRER
                                       ----------------------------------
                                      Name: James A. Harrer
                                      Title: President

                                   By: /s/ DONALD M. LEONARD
                                       ----------------------------------
                                      Name: Donald M. Leonard
                                      Title: Chief Financial Officer &
                                             Vice President

                                       5
<PAGE>   7
                               STATE OF DELAWARE
                                                                          PAGE 1
                        OFFICE OF THE SECRETARY OF STATE

                        --------------------------------

     I, EDWARD J. FREEL, SECRETARY OF STATE OF THE STATE OF DELAWARE, DO HEREBY
CERTIFY THE ATTACHED IS A TRUE AND CORRECT COPY OF THE CERTIFICATE OF MERGER,
WHICH MERGES:

     "MUSTANG.COM ACQUISITION CORPORATION", A DELAWARE CORPORATION,

     WITH AND INTO "MUSTANG.COM, INC." UNDER THE NAME OF "MUSTANG.COM, INC.", A
CORPORATION ORGANIZED AND EXISTING UNDER THE LAWS OF THE STATE OF CALIFORNIA,
AS RECEIVED AND FILED IN THIS OFFICE THE EIGHTEENTH DAY OF MAY, A.D. 2000, AT
9 O'CLOCK A.M.

     A FILED COPY OF THIS CERTIFICATE HAS BEEN FORWARDED TO THE NEW CASTLE
COUNTY RECORDER OF DEEDS.

                                      /s/ EDWARD J. FREEL
                       [SEAL]         ------------------------------------------
                                        Edward J. Freel, Secretary of State

                                      AUTHENTICATION: 0453683

                                                DATE: 05-23-00
<PAGE>   8
                                                           STATE OF DELAWARE
                                                           SECRETARY OF STATE
                                                        DIVISION OF CORPORATIONS
                                                       FILED 09:00 AM 05/18/2000
                                                           001257237 - 3231346

                             CERTIFICATE OF MERGER
                                       OF
                      MUSTANG.COM ACQUISITION CORPORATION
                                      AND
                               MUSTANG.COM, INC.

It is hereby certified that:

1. The constituent business corporations participating in the merger herein
certified are:

     (i)  Mustang.com Acquisition Corporation, which is incorporated under the
          laws of the State of Delaware; and

     (ii) Mustang.com, Inc., which is incorporated under the laws of the State
          of California.

2. An agreement and plan of merger has been approved, adopted, certified,
executed and acknowledged by each of the aforesaid constituent corporations in
accordance with the laws under which it is formed, pursuant to Section 252 of
the Delaware General Corporation Law.

3. The name of the surviving corporation in the merger herein certified is
Mustang.com, Inc., which will continue its existence as said surviving
corporation under its present name upon the effective date of said merger
pursuant to the provisions of the laws of the State of its incorporation.

4. The certificate of incorporation of Mustang.com, Inc., as now in force and
effect, shall continue to be the certificate of incorporation of said surviving
corporation until amended and changed pursuant to the provisions of the laws of
the State of its incorporation.

5. The executed agreement and plan of merger between the aforesaid constituent
corporations is on file at an office of the aforesaid surviving corporation, the
address of which is as follows:

                             Mustang.com, Inc.
                             6200 Lake Ming Road
                             Bakersfield, CA 93306

6. A copy of the aforesaid agreement and plan of merger will be furnished by the
aforesaid surviving corporation, on request, and without cost, to any
stockholder of each of the aforesaid constituent corporations.
<PAGE>   9
7. The aforesaid surviving corporation does hereby agree that it may be served
with process in the State of Delaware in any proceeding for enforcement of any
obligation of Mustang.com Acquisition Corporation, as well as for enforcement of
any obligation of said surviving corporation arising from the merger herein
certified, including any suit or other proceeding to enforce the right, if any,
of any stockholder of Mustang.com Acquisition Corporation as determined in
appraisal proceedings pursuant to the provisions of Section 262 of the General
Corporation Law of the State of Delaware; does hereby irrevocably appoint the
Secretary of State of the State of Delaware as its agent to accept service of
process in any such suit or other proceedings; and does hereby specify the
following as the address to which a copy of such process shall be mailed by the
Secretary of State of the State of Delaware:

                           Quintus Corporation
                           47212 Mission Falls Court
                           Fremont, CA 94539

8. The agreement and plan of merger between the aforesaid constituent
corporations provides that the merger herein certified shall be effective at
such time as this certificate is filed with the Secretary of State of the State
of Delaware.
<PAGE>   10
Dated: May 18, 2000

                                             MUSTANG.COM ACQUISITION CORPORATION

                                             By:
                                                 -------------------------------
                                                 Name: Alan K. Anderson
                                                 Title: President

Dated: May 18, 2000

                                             MUSTANG.COM INC.

                                             By: /s/ JAMES A. HARRER
                                                 -------------------------------
                                                 Name: James A. Harrer
                                                 Title: President & CEO
<PAGE>   11
Dated: May 18, 2000

                                             MUSTANG.COM ACQUISITION CORPORATION

                                             By: /s/ ALAN K. ANDERSON
                                                 -------------------------------
                                                 Name: Alan K. Anderson
                                                 Title: President

Dated: May 18, 2000

                                             MUSTANG.COM INC.

                                             By:
                                                 -------------------------------
                                                 Name:
                                                 Title:<PAGE>   1
                                                                   EXHIBIT 10.22

                                PROMISSORY NOTE

$4,880,700                                                        April 27, 2000
                                                             Fremont, California

     FOR VALUE RECEIVED, the undersigned Borrower promises to pay to Quintus
Corporation, (the "Company"), at its principal offices at 47212 Mission Falls
Court, Fremont, California, the principal sum of four million eight hundred
eighty thousand seven hundred dollars ($4,880,700), which sum Borrower has
received in connection with the exercise of his option, upon the terms and
conditions specified below.

     1.   Principal. The principal balance of this Note together with all
accrued and unpaid interest owing hereunder shall be due and payable in full on
April 26, 2004.

     2.   Rate of Interest. Interest shall accrue under the Note on any unpaid
principal balance at the rate of 6.71 percent (6.71%) per annum, compounded
annually.

     3.   Prepayment. Prepayment of principal and accrued interest may be made
at any time without penalty.

     4.   Events of Acceleration. The entire unpaid principal sum of this Note
and accrued interest shall become immediately due and payable upon one or more
of the following events:

          A.   180 days after Borrower's last day of employment by the Company;
or

          B.   the failure of the Borrower to pay when due the principal balance
and accrued interest owing under this Note; or

          C.   the filing of a petition by or against Borrower under any
provisions of the Bankruptcy Reform Act, Title 11 of the United States Code, as
amended or recodified from time to time, or under any similar or other law
relating to bankruptcy, insolvency, reorganization or other relief for debtors;
the appointment of a receiver, trustee, custodian or liquidator of or for any
part of the assets or property of Borrower; the execution by the Borrower of a
general assignment for the benefit of creditors; the insolvency of Borrower or
Borrower is generally not paying its debts as they become due; or any attachment
or like levy on any property of Borrower; or

          D.   the occurrence of an event of default under the Stock Pledge
Agreement dated as of the date hereof.

     5.   Security. Borrower's obligations under this Note shall be secured by a
first priority security interest in all shares of Company common stock acquired
by Borrower pursuant to the option exercise for which this loan is extended
("Stock") and such shares of Stock shall be pledged pursuant to the Stock Pledge
Agreement to be executed by Borrower in the form of Schedule A hereto, all terms
of which are incorporated herein by this reference.
<PAGE>   2
Regardless of any collateral that may secure Borrower's obligations under the
Note, Borrower shall remain personally liable for the payment in full of any
indebtedness owing under this Note, and the Company shall have recourse to any
and all other assets of the Borrower, in addition to any shares of Stock pledged
pursuant to the terms and provisions of the Stock Pledge Agreement, to satisfy
Borrower's obligations hereunder.

     6.   Costs and Expenses; Attorneys' Fees. If any action is instituted to
collect this Note, the Borrower promises to pay all reasonable costs and
expenses (including reasonable attorneys' fees) incurred by the Company in
connection with the enforcement of the Company's rights and/or the collection of
any amounts that become due to the Company under this Note.

     7.   Waiver. No previous waiver and no failure or delay by the Company or
Borrower in acting with respect to the terms of this Note or the Stock Pledge
Agreement shall constitute a waiver of any breach, default, or failure of
condition under this Note or the Stock Pledge Agreement executed in connection
herewith or the obligations secured thereby. A waiver of any term of this Note,
the Stock Pledge Agreement, or of any of the obligations secured thereby must be
made in writing and signed by a duly authorized officer of the Company and shall
be limited to the express terms of such waiver. Borrower hereby expressly waives
presentment and demand for payment at such time as any payments are due under
this Note.

     8.   Conflicting Agreements. In the event of any inconsistencies between
the terms of this Note and the terms of any other document related to the loan
evidenced by the Note, the terms of this Note shall prevail.

     9.   Governing Law. This Note shall be construed in accordance with the
laws of the State of California.

Signature of Borrower:

/s/ PAUL BARTLETT
---------------------------
Paul Bartlett

Address:
         ------------------

         ------------------

                                       2
<PAGE>   3
                             STOCK PLEDGE AGREEMENT

          In order to secure payment of all obligations of Paul Bartlett
("Borrower") to Quintus Corporation, a Delaware corporation (the "Company")
having its corporate offices at 47212 Mission Falls Court, Fremont, California,
under that certain promissory note dated May 1, 2000 in the original principal
amount of $4,880,700 (the "Note") executed by Borrower in favor of the Company,
Borrower hereby grants to the Company a security interest in, and assigns,
transfers to and pledges with the Company, the following securities and other
property:

               (i)   the 550,000 shares of Company common stock ("Common Stock")
previously delivered to and deposited with the Company as collateral for the
Note; and

               (ii)  any and all new, additional or different securities or
other property subsequently distributed with respect to the shares identified in
subparagraph (i) that are to be delivered to and deposited with the Company
pursuant to the requirements of paragraph 3 of this Agreement; and

               (iii) any and all other property and money that is delivered to
or comes into the possession of the Company pursuant to the terms and provisions
of this Agreement; and

               (iv)  the proceeds of any sale, exchange or disposition of the
property and securities described in subparagraphs (i), (ii) or (iii) above, net
of income taxes.

          All of the foregoing property together with any securities, property
and money to be assigned to, transferred to and pledged with the Company shall
be herein referred to as the "Collateral" and shall be accompanied by one or
more stock power assignments properly endorsed to the Company by the Borrower.
The Company shall hold the Collateral in accordance with the following terms and
provisions:

     1.   Warranties. The Borrower hereby warrants to the Company that the
Borrower is the owner of the Collateral and has the right to pledge the
Collateral and that the Collateral is free from all liens, advance claims and
other security interests (other than those created hereby).

     2.   Rights and Powers. The Company may, without obligation to do so,
exercise one or more of the following rights and powers with respect to the
Collateral:

               (a)  accept in its discretion, but subject to the applicable
limitations of paragraphs 7(a), (c) and (d), other property of the Borrower in
exchange for all or part of the Collateral and release Collateral to the
Borrower to the extent necessary to effect such exchange, and in such event the
money, property or securities received in the exchange shall be held by the
Company as substitute security for the Note and all other indebtedness secured
hereunder;

               (b)  perform such acts as are necessary to preserve and protect
the Collateral and the rights, powers and remedies granted with respect to such
Collateral by this Agreement; and
<PAGE>   4
               (c)  transfer record ownership of the Collateral to the Company
or its nominee and receive, endorse and give receipt for, or collect by legal
proceedings or otherwise, dividends or other distributions made or paid with
respect to the Collateral, provided and only if there exists at the time an
outstanding event of default under paragraph 8 of this Agreement.

          Any action by the Company pursuant to the provisions of this paragraph
2 may be taken without notice to the Borrower. Any costs or expenses (including
reasonable attorneys' fees) reasonably incurred in connection with any such
action shall be payable by the Borrower and form part of the indebtedness
secured hereunder as provided in paragraph 10.

          So long as there exists no event of default under paragraph 8 of this
Agreement, the Borrower may exercise all shareholder voting rights and be
entitled to receive any and all regular cash dividends paid on the Collateral.
Accordingly, until such time as an event of default occurs under this Agreement,
all proxy statements and other shareholder materials pertaining to the
Collateral shall be delivered to the Borrower at the address indicated below;
provided however, if an event of default has occurred hereunder and is
continuing, any or all Collateral may be registered, without notice, in the name
of the Company or its nominee, and thereafter the Company or its nominee may
exercise, without notice, all voting and corporate rights at any meeting of the
shareholders of the Company thereof, any and all rights of conversion, exchange
or subscription, or any other rights, privileges or options pertaining to the
Collateral, all as if the Company were the absolute owner thereof.

          Any cash sums that the Company may receive in the exercise of its
rights and powers under paragraph 2(b) above shall be applied to the payment of
the Note and any other indebtedness secured hereunder, in such order of
application as the Company deems appropriate. Any remaining cash shall be paid
over to the Borrower.

     3.   Duty to Deliver.  Any new, additional or different securities that may
now or hereafter become distributable with respect to the Collateral by reason
of (i) any stock dividend, stock split or reclassification of the capital stock
of the Company, or (ii) any merger, consolidation or other reorganization
affecting the capital structure of the Company, shall, upon receipt by the
Borrower, be promptly delivered to and deposited with the Company as part of
the Collateral hereunder. Such securities shall be accompanied by one or more
properly-endorsed stock power assignments.

     4.   Care of Collateral.  The Company shall exercise reasonable care in the
custody and preservation of the Collateral, but shall have no obligation to
initiate any action with respect to, or otherwise inform the Borrower of, any
conversion, call, exchange right, preemptive right, subscription right, purchase
offer or other right or privilege relating to or affecting the Collateral;
provided, however, that the Company will notify the Borrower of any such rights
of the Borrower to protect against adverse claims or to protect the Collateral
against the possibility of a decline in market value. The Company shall not be
obligated to take any action with respect to the Collateral requested by the
Borrower unless the request is made in writing and the Company determines that
the requested action will not unreasonably jeopardize the value of the
Collateral as security for the Note and other indebtedness secured hereunder.

                                       2
<PAGE>   5
            The Company may at any time release and deliver all or part of the
Collateral to the Borrower, and the receipt thereof by the Borrower shall
constitute a complete and full acquittance for the Collateral so released and
delivered. The Company shall accordingly be discharged from any further
liability or responsibility for the Collateral, and the released Collateral
shall no longer be subject to the provisions of this Agreement. However, any and
all releases of the Collateral shall be effected in compliance with the
applicable limitations of paragraphs 7(a) and 7(c).

      5.    Payment of Taxes and Other Charges. The Borrower shall pay, prior to
the delinquency date, all taxes, liens, assessments and other charges against
the Collateral, and in the event of the Borrower's failure to do so, the Company
may at its election pay any or all of such taxes and charges without contesting
the validity or legality thereof. The payments so made shall become part of the
indebtedness secured hereunder and until paid shall bear interest at the minimum
per annum rate, compounded annually, required to avoid the imputation of
interest income to the Company and compensation income to the Borrower under the
federal tax laws.

      6.    Transfer of Collateral. In connection with the transfer or
assignment of all or part of the indebtedness evidenced by the Note (whether by
negotiation, discount or otherwise), the Company may transfer all or any part of
the Collateral, and the transferee shall thereupon succeed to all the rights,
powers and remedies granted the Company hereunder with respect to the Collateral
so transferred. Upon such transfer, the Company shall be fully discharged from
all liability and responsibility for the transferred Collateral. With respect to
any Collateral not transferred, the Company shall retain all rights, powers,
privileges and remedies provided herein.

      7.    Release of Collateral. Provided (i) all indebtedness secured
hereunder (other than payments not yet due and payable under the Note) shall at
the time have been paid in full or cancelled and (ii) there does not otherwise
exist any event of default under paragraph 8, the pledged shares of Common
Stock, together with any additional Collateral that may hereafter be pledged and
deposited hereunder, shall be released from pledge and returned to the Borrower
in accordance with the following provisions:

            (a)   Upon payment or prepayment of principal under the Note,
together with payment of all accrued interest to date, one or more shares of
Common Stock held as Collateral hereunder shall (subject to the applicable
limitations of paragraphs 7(c) and (d) below) be released to the Borrower within
three (3) days after such payment or prepayment. The number of shares to be so
released shall be equal to the number obtained by multiplying (i) the total
number of shares of Common Stock held under this Agreement at the time of the
payment or prepayment, by (ii) a fraction of the numerator of which shall be the
amount of the principal paid or prepaid and the denominator of which shall be
the unpaid principal balance of the Note immediately prior to such payment or
prepayment. In no event, however, shall any fractional shares be released. In
addition, one or more shares of Common Stock held as Collateral hereunder shall
(subject to the applicable limitations of paragraphs 7(c) and (d) below) be
released to a stock broker designated in writing by the Borrower and acceptable
to the Company for the sole purpose of effecting an immediate sale of the
released shares and provided that such stock broker agrees to forward any
proceeds (up to the balance of principal and interest due under the Note)
directly to the Company to be used to satisfy the Note.

                                       3
<PAGE>   6
            (b)   Any additional Collateral that may hereafter be pledged and
deposited with the Company (pursuant to the requirements of paragraph 3) with
respect to the shares of Common Stock pledged hereunder shall be released at
the same time the particular shares of Common Stock to which the additional
Collateral relates are to be released in accordance with the applicable
provisions of paragraph 7(a). Under no circumstances, however, shall any shares
of Common Stock or any other Collateral be released if previously applied to
the payment of any indebtedness secured hereunder.

            (c)   In no event, however, shall any shares of Common Stock be
released pursuant to the provisions of paragraph 7(a) or 7(b) if, and to the
extent, the fair market value of the Common Stock and all other Collateral that
would otherwise remain in pledge hereunder after such release were affected
would be less than the unpaid balance of the Note (principal and accrued
interest).

            (d)   In the event the securities constituting the Collateral
become "margin securities" (within the meaning of Section 207.2(i) of
Regulation G of the Federal Reserve Board), then the value of the Collateral
securing the Note shall not be less than fifty percent (50%) of the current
market value of such securities. Accordingly, the number of shares to be
released pursuant to paragraph 7(a) or (b) shall be reduced to the extent
necessary to comply with Regulation G.

      8.    Events of Default. The occurrence of one or more of the following
events shall constitute an event of default under this Agreement:

            (a)   any default in the payment or performance of any obligation
or any defined event of default under the Note.

            (b)   Borrower shall fail to perform any obligation or agreement
contained herein; or

            (c)   any warranty made by Borrower herein shall prove to be
incorrect, false or misleading in any material respect; and

            (d)   any attachment or like levy on any property of Borrower.

      Upon the occurrence of any such event of default, the Company may, at its
election, declare the Note and all other indebtedness secured hereunder to
become immediately due and payable and may exercise any or all of the rights
and remedies granted to a secured party under the provisions of the California
Uniform Commercial Code (as now or hereafter in effect), including (without
limitation) the power to dispose of the Collateral by public or private sale or
to accept the Collateral in full payment of the Note and all other indebtedness
secured hereunder.

      Any proceeds realized from the disposition of the Collateral pursuant to
the foregoing power of sale shall be applied first to the payment of reasonable
expenses incurred by the Company in connection with the disposition, then to
the payment of the Note and finally to any other indebtedness secured
hereunder. Any surplus proceeds shall be paid over to the Borrower. However, in
the event such proceeds prove insufficient to satisfy all obligations of

                                       4
<PAGE>   7
the Borrower under the Note, then the Borrower shall remain personally liable
for the resulting deficiency.

      9.    Certain Waivers. Borrower waives, to the fullest extent permitted by
law, (i) any right of redemption with respect to the Collateral, whether before
or after sale hereunder, and all rights, if any, of marshalling of the
Collateral or other collateral or security for Borrower's obligations under the
note; (ii) any right to require the Company (a) to proceed against any other
person or entity, (b) to exhaust any other collateral or security for any of the
Borrower's obligations under the Note, (c) to pursue any remedy in the Company's
power, (d) to make or give any presentments, demands for performance, notices of
nonperformance, protests, notices of protests or notices of dishonor in
connection with any of the Collateral, (e) to direct the application of payments
or security for any obligations of Borrower under the Note; and (iii) all
claims, damages, and demands against the Company arising out of the
repossession, retention, sale or application of the proceeds of any sale of the
Collateral.

      10.   Other Remedies. The rights, powers and remedies granted to the
Company and Borrower pursuant to the provisions of this Agreement shall be in
addition to all rights, powers and remedies granted to the Company and Borrower
under any statute or rule of law. Any forbearance, failure or delay by the
Company or Borrower in exercising any right, power or remedy under this
Agreement shall not be deemed to be a waiver of such right, power or remedy. Any
single or partial exercise of any right, power or remedy under this Agreement
shall not preclude the further exercise thereof, and every right, power and
remedy of the Company and Borrower under this Agreement shall continue in full
force and effect unless such right, power or remedy is specifically waived by an
instrument executed by the Company or Borrower, as the case may be.

      11.   Costs and Expenses. All reasonable costs and expenses (including
reasonable attorneys' fees) incurred by the Company in the exercise or
enforcement of any right, power or remedy granted it under this Agreement shall
become part of the indebtedness secured hereunder and shall constitute a
personal liability of the Borrower payable immediately upon demand and bearing
interest until paid at the Company's bank interest rate then being earned by the
Company on its deposits.

      12.   Applicable Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of California and shall be binding upon
the executors, administrators, heirs and assigns of the Borrower.

      13.   Arbitration. Any controversy between the parties hereto involving
the construction or application of any terms, covenants or conditions of this
Agreement or the Note, or any claims arising out of or relating to this
Agreement or the Note, or the breach hereof or thereof, will be submitted to and
settled by final and binding arbitration in Santa Clara, California, in
accordance with the rules of the American Arbitration Association then in
effect, and judgment upon the award rendered by the arbitrator may be entered in
any court having jurisdiction thereof. In the event of any arbitration under
this Agreement or the Note, the prevailing party shall be entitled to recover
from the losing party reasonable expenses, attorneys' fees, and costs incurred
therein or in the enforcement or collection of any judgment or award rendered
therein. The "prevailing party" means the party determined by the arbitrator to
have

                                       5
<PAGE>   8
most nearly prevailed, even if such party did not prevail in all matters, not
necessarily the one in whose favor a judgment is rendered.

     14.  Severability. If any provision of this Agreement is held to be
invalid under applicable law, then such provision shall be ineffective only to
the extent of such invalidity, and neither the remainder of such provision nor
any other provisions of this Agreement shall be affected hereby.

     IN WITNESS WHEREOF, this Agreement has been executed by the Borrower on
this 27 day of April, 2000.

                                        /s/  PAUL BARTLETT
                                        --------------------------------
                                        Signature of Borrower
                                        Paul Bartlett

                                        Address:
                                                  ----------------------
                                                  ----------------------

Agreed to and Accepted by:

QUINTUS CORPORATION

By: /s/  SUSAN SALVESEN
   -------------------

Title:  CFO
     -----------------

Dated:  4/27, 2000
     -----------------

                                       6

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