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                                                                   EXHIBIT 10.42

                             CO-MARKETING AGREEMENT

                  THIS MARKETING AGREEMENT (this "Agreement"), dated this 4th
day of November, 1999 (the "Effective Date"), is by and between priceline.com
Incorporated, a Delaware corporation ("priceline"), and Net2Phone, Inc., a
Delaware corporation ("Carrier").

                                    RECITALS

                  WHEREAS, priceline is in the business of providing airline
tickets and other consumer products and services to consumers primarily through
the Internet;

                  WHEREAS, Carrier is in the business of providing Internet
protocol telephone services; and

                  WHEREAS, priceline and Carrier desire to enter into a
co-marketing arrangement.

                  NOW THEREFORE, in consideration of the mutual covenants and
agreements contained herein, the parties hereto agree as follows:

                                   ARTICLE I
                                   PROMOTIONS

         1.1 Description of Promotion. The promotion (the "Best Efforts Card
Promotion") will be operated by priceline commencing on or before [****] and
expiring on [****]. The Best Efforts Card Promotion will be offered to selected
customers of priceline who have made a reasonable offer for an airline ticket
through priceline's demand collection service for airline tickets but have
failed to have their offer accepted. Under the Best Efforts Card Promotion,
Priceline will contact selected customers and provide them the ability to
improve their chances of having their offer accepted if they agree to increase
their offer price by a dollar amount determined by Priceline and agree to apply
for a free [****]Carrier calling card account. Priceline will disclose that such
accounts will be automatically renewed when the balance drops below [****] and
charged by Carrier to the customer's credit card unless deactivated by customer.
Within 72 hours following each customer's electing to participate in the Best
Efforts Card Promotion, Carrier shall provide an activated [****] calling card
account number. Each calling card account will be provided by Carrier free of
charge to the customer and/or Priceline.

         1.2 Compensation. [****] The [****] shall be payable immediately upon
the execution of this Agreement. [****] shall be payable within 15 days
following priceline's delivery of the invoice thereof.

         1.3 Priceline shall deliver [****] activated new calling card accounts
during the Term. Upon activation such Priceline customers also become customers
of Carrier. In the event Priceline fails to deliver the [****] activated new
calling card accounts during the Term, Priceline agrees to continue the
Promotion until said level is achieved.
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                                   ARTICLE II
                               RECORDS AND REPORTS

         2.1 Records. Each party shall maintain accurate records with respect to
whether the participating customers are completing their obligations under the
applicable promotion including, without limitation, maintaining records
necessary for the parties to verify the amount of compensation to be paid to
priceline under this Agreement. The parties shall cooperate to prepare and
provide to each other such other records and reports that either party may
reasonably request. All such records shall be open for inspection and audit by
representatives and agents of the parties during normal business hours.

                                  ARTICLE III
                                 PRIVACY POLICY

             Carrier agrees that under no circumstances will it use, disclose or
disseminate any customer identifying information collected in the application
process of the Best Efforts Card Promotion in violation of current and/or
further consumer privacy legislation or priceline's privacy policy in effect
from time to time. In addition, Carrier acknowledges and agrees that without
Carrier first obtaining the prior written consent of a subject customer (i)
Carrier will not sell, transfer, share or otherwise disclosed to any third party
any individual customer's information obtained by, or provided to, Carrier in
connection with this Agreement, including, without limitation, any customer's
name, mailing address, e-mail address or telephone number or credit card
information.

                                   ARTICLE IV
                                TERM; TERMINATION

         4.1 Term. The term of this Agreement (the "Term") shall commence on the
Effective Date and shall terminate on [****].

                                   ARTICLE V
                                 INDEMNIFICATION

         5.1 Indemnity. Each party shall indemnify, defend, and hold harmless
the other and its affiliates, officers, agents, and employees, from all claims,
suits, actions, demands, damages, liabilities, expenses (including reasonable
fees and disbursements of counsel), judgments, settlements and penalties of
every kind to the extent resulting from, arising out of, or incurred in
connection with (a) any breach by such party of any representation, warranty,
covenant, agreement or other obligation contained herein; and/or (b) the
negligent, intentionally wrongful or illegal acts or omissions of such party,
its employees, agents, subcontractors or other representatives and/or (c)
violations of any federal, state, local and/or international laws, rules and/or
regulations to which such party is subject.

         5.2 Indemnification Procedures. The Indemnified Party shall notify the
Indemnifying Party in writing of any suits, claims or demands covered by this
indemnity promptly after becoming aware of such suits, claims or demands.
Promptly after receipt of such notice, the Indemnifying Party shall assume the
defense of such claim with counsel reasonably satisfactory to the Indemnified
Party. If the Indemnifying Party fails, within a reasonable time after receipt

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of such notice, to assume the defense with counsel reasonably satisfactory to
the Indemnified Party, or if, in the reasonable judgment of the Indemnified
Party, a direct or indirect conflict of interest exists between the parties with
respect to the claim, or if in the sole judgment of the Indemnified Party the
assumption and conduct of the defense by the Indemnified Party would materially
and adversely affect the Indemnified Party in any manner or prejudice its
ability to conduct a successful defense, then the Indemnified Party shall have
the right to undertake the defense, compromise and settlement of such claim for
the account and at the expense of the Indemnifying Party. Notwithstanding the
above, if the Indemnified Party in its sole discretion so elects, the
Indemnified Party may also participate in the defense of such actions by
employing counsel at its expense, without waiving the Indemnified Party's
obligations to indemnify or defend. The Indemnifying Party shall not settle or
compromise any claim or consent to the entry of any judgment without the prior
written consent of the Indemnified Party and without an unconditional release of
all liability by each claimant or plaintiff to the Indemnified Party.

         5.3 Limitations of Liability.

                  NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR ANY INDIRECT,
INCIDENTAL, RELIANCE, SPECIAL, PUNITIVE OR CONSEQUENTIAL DAMAGES, INCLUDING LOSS
OF PROFITS, REVENUE, PROSPECTIVE BUSINESS, DATA, OR USE, INCURRED BY EITHER
PARTY, WHETHER IN AN ACTION IN CONTRACT OR TORT, EVEN IF THE OTHER PARTY OR ANY
OTHER PERSON HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

         5.4 The provisions of this Article V shall survive any termination of
this Agreement.

                                   ARTICLE VI
                            MISCELLANEOUS PROVISIONS

         6.1 Relationship of the Parties. Nothing in this Agreement is intended
to or shall be construed to constitute or establish an agency, joint venture,
partnership or fiduciary relationship between the parties, and neither party
shall have the right or authority to act for or on behalf of the other party.

         6.2 Waiver; Modification. No provision of this Agreement may be
modified, waived or discharged unless such waiver, modification or discharge is
agreed to in writing and signed by a duly authorized representative of each of
the parties hereto. No waiver by either party hereto at any time of any breach
by the other party hereto of, or compliance with, any condition or provision of
this Agreement to be performed by such other party shall be deemed a waiver of
similar or dissimilar provisions or conditions at the same or at any prior or
subsequent time.

         6.3 Invalidity. If any provision of this Agreement shall be determined
by any court of competent jurisdiction to be unenforceable or invalid to any
extent, the remainder of this Agreement shall not be affected thereby, and this
Agreement shall be construed to the fullest extent possible so as to give effect
to the intentions of the provision found unenforceable or invalid.

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         6.4 Notices. All notices and other communications provided for
hereunder shall be in writing and shall be delivered to each party hereto at the
address set forth on the signature page hereto. Such notices shall be deemed to
be effective five (2) business days after the same shall be deposited, postage
prepaid, in the mail.

         6.5 Governing Law. The validity, interpretation, construction and
performance of this Agreement shall be governed by the laws of the State of New
York without regard to its conflicts of law principles.

         6.6 Counterparts. This Agreement may be executed in counterparts, each
of which shall be deemed to be an original but all of which together will
constitute one and the same instrument.

         6.7 Headings. All headings contained in this Agreement are for
reference purposes only and shall not in any way effect the meaning or
interpretation of any provision or provisions of this Agreement.

              INTENTIONALLY LEFT BLANK - THE SIGNATURE PAGE IS NEXT

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                  IN WITNESS WHEREOF, the parties hereto have duly executed this
Agreement as of the day and year first above written.

                               PRICELINE.COM INCORPORATED

                               By: /s/ Daniel H. Schulman
                               Name: Daniel H. Schulman
                               Title: President and Chief Operating Officer

                               Address Notices to:
                               Five High Ridge Park
                               Stamford, CT 06905
                               Attn: General Counsel

                               NET2PHONE, INC.

                               By: /s/ Howard Balter
                               Name: Howard Balter
                               Title: Chief Executive Officer

                               Address Notices to:
                               171 Main Street
                               Hackensack, NJ 07601
                               Attn: Scott Sobel, Director Business Development
                               Cc: General Counsel

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                                                                   EXHIBIT 10.43

                       AMENDMENT TO CO-MARKETING AGREEMENT

         This Amendment is made this 31st day of March, 2000, between
priceline.com, Incorporated ("priceline"), with offices at 800 Connecticut
Avenue, Norwalk, Connecticut 06854, and Net2Phone, Inc. ("Net2Phone") with
offices at 171 Main Street, Hackensack, New Jersey 07601.

         WHEREAS, the parties entered into a Co-Marketing Agreement dated
November 4, 1999 (the "Agreement"); and

         WHEREAS, the parties now desire to memorialize their mutual
understanding to amend the Agreement and MOU as set forth herein.

         NOW THEREFORE, in consideration of the mutual covenants and agreements
contained herein, the parties hereto agree as follows:

                           1. Section 1.2 of the Agreement is amended to provide
                  that [****] (collectively the "Fee") during priceline's fiscal
                  fourth quarter ended December 31, 1999.

                           2. The fee has been paid in full to [****].

         In all other respects he terms of the Agreement shall remain unchanged.

         IN WITNESS WHEREOF, the parties hereto have duly executed this
Agreement as of the day and year first above written.

PRICELINE.COM INCORPORATED                      NET2PHONE, INC.

By: /s/ Robert Mylod                            By: /s/ Ilan Slasky
Name: Robert Mylod                              Name: Ilan Slasky
Title: Senior Vice President-Finance            Title: Chief Financial Officer

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