<PAGE>

                                                                 Exhibit 10.30

                       [iBasis, Inc. Letterhead]


                                                            September 17, 2001



Richard G. Tennant
10703 Miller Road
Oakton, VA 22124

Dear Mr. Tennant,

We are pleased to offer you the position of Chief Financial Officer at iBasis,
Inc. This position is located in Burlington, MA. You will report to Ofer
Gneezy, Chief Executive Officer.

Your salary will be $175,000 per annum, earned and payable at the
semi-monthly rate of $7,291.66. Your annual incentive compensation, based on
individual and corporate performance, will be up to $87,500. We will outline
the specific details of your incentive compensation within a reasonable time
after your start date.

You will also be provided with relocation assistance for your move from
Virginia to the Burlington area. Details of the relocation assistance will
follow shortly.

You will be eligible to receive a comprehensive benefits package including:
Medical and Dental insurance at nominal cost to the employee, Employee Stock
Purchase Plan, Section 125 Flexible Spending Accounts, an employer-matched
401(k) plan, tuition reimbursement, Company-paid life/disability and group
travel accident insurance, three weeks accrued vacation and eleven (11)
holidays.

In addition, a recommendation will be made to the Board of Directors to grant
you 150,000 shares of iBasis Inc. Incentive Stock Options. The Compensation
Committee of the Board of Directors meets at the end of the quarter to
approve grants. The option price is based on fair market value. You will
receive a copy of the stock plan and your option grant agreement within
ninety (90) days of its approval by the Board. These options vest over a
four-year period.

If iBasis terminates your employment without cause, or if you terminate your
employment with "good reason," in either case within six months after the
occurrence of an acquisition or change in control, then your stock options
will immediately vest and iBasis will continue to pay your salary for nine
months. Such vesting and payment are subject to the terms and conditions
generally applicable within iBasis for such policies.

Enclosed, please find a copy of iBasis' "Proprietary Information and
Inventions Agreement". Upon joining the Company, we ask you to provide us
with a signed copy of this document.

Additionally, we are required by the Immigration Reform and Control Act
(IRCA), to ask you to provide proof that you are authorized to work in the
U.S.

<PAGE>

Dick, we look forward to you joining our senior executive team and being part
of our continued leadership in Internet based communications.

We look forward to your formal acceptance of this offer. Please sign and
return the duplicate letter to Tamah Rosker, Vice President, Human Resources.
This offer will remain open until September XX, 2001.

Sincerely,

/s/ Ofer Gneezy

Ofer Gneezy
Chief Executive Officer

I accept this offer of employment and will begin work on Monday, October 22,
2001.

Signature:  /s/ Richard G. Tennant               Date:   Sept. 20, 2001
          ---------------------------               ---------------------

<PAGE>

                           IBASIS EMPLOYMENT AGREEMENT

         This Employment Agreement (the "AGREEMENT") is made and entered into by
and between iBasis, Inc., a Delaware corporation having its principal place of
business at 20 Second Avenue, Burlington, MA 01803 (together with its successors
and assigns, and any of its present or future subsidiaries, or organizations
controlled by, controlling or under common control with it, the "COMPANY") and
its Employee (the "EMPLOYEE").

                                    RECITALS

         WHEREAS, the Company recognizes that the Employee's talents and
liabilities are unique and valuable, and thus wishes to secure the services of
the Employee on the terms and conditions set forth herein; and

         WHEREAS, the Company desires to engage the Employee based on the
Employee's particular qualifications, in a capacity in which the Employee may
receive, initiate, contribute to or come in contact with Confidential and
Proprietary Information (as hereinafter defined), and the Employee desires to be
engaged in such a capacity; and

         WHEREAS, the Employee specifically acknowledges that this engagement
may include inventing, discovering, initiating or contributing to Confidential
or Proprietary Information and that the rights to such information are intended
to belong solely to the Company;

         NOW, THEREFORE, in consideration of the mutual promises and conditions
hereinafter contained, and other good and valuable consideration the receipt and
sufficiency of which is hereby acknowledged, the parties hereto agree as
follows:


SECTION 1.        EMPLOYMENT.

         1.1      EMPLOYMENT. The Company hereby agrees to employ the Employee
                  under the terms set forth in this Agreement and the letter
                  confirming employment sent to Employee by the Company.

         1.2      DUTIES. The Employee shall have such duties as are assigned to
                  the Employee by the Company. The Employee agrees to use the
                  Employee's best efforts to promote the success of the
                  Company's business, and to advance the best interests of the
                  Company. The Employee shall devote substantially all of the
                  Employee's working time, attention and energies during normal
                  business hours (other then absences due to illness or
                  vacation) to the performance of the Employee's duties for the
                  Company. During the term of the Employee's employment with the
                  Company, the Employee will not engage in any other employment
                  or consulting activities for any third party for direct or
                  indirect remuneration without written consent of the Company.

         1.3      SALARY. During the Employee's engagement by the Company, the
                  Company will pay the Employee an annual salary, to be paid in
                  accordance with the Company's payroll practices and policies
                  and subject to applicable withholdings. "Exempt" positions are
                  exempt from overtime pay, and the Employee's salary will
                  compensate the Employee for all hours worked. "Non-exempt"
                  positions will be eligible to earn overtime on any time in
                  excess of forty (40) hours worked in a week.

SECTION 2.        TERM.

         There is no specified length of employment. Accordingly, either the
Employee or the Company may terminate the employment relationship at will, with
or without cause, at any time. In conjunction with this policy of "at-will"
employment, the Employee may also be disciplined, demoted or have her or his job
responsibilities reassigned by the Company for any reason at the Company's sole
discretion.


<PAGE>

SECTION 3.        INVENTIONS AND OTHER INTELLECTUAL PROPERTY

         3.1      DEFINITIONS. As used in this Agreement, the term "COMPANY'S
                  FACILITIES, MATERIAL OR PERSONNEL" means facilities, material
                  or personnel owned, leased, occupied or controlled by the
                  Company as well as the facilities, materials or personnel of
                  third parties rented, leased or otherwise hired by the Company
                  for the conduct of aspects of the business of the Company, and
                  the term "INVENTIONS AND OTHER INTELLECTUAL PROPERTY" means
                  inventions, discoveries, concepts, developments, and ideas,
                  whether patentable or not, including but not limited to
                  software and hardware systems and services, devices,
                  processes, methods, formulae, and works of authorship
                  including computer programs, and operations, training and
                  maintenance manuals.

         3.2      OWNERSHIP. The Employee hereby agrees that all right, title
                  and interest in and to all of the Employee's Inventions and
                  Other Intellectual Property made during the period of
                  employment with the Company, whether pursuant to this
                  Agreement or otherwise, and whether or not during the hours of
                  the Employee's engagement or with the use or assistance of
                  Company Facilities, Materials or Personnel, either solely or
                  jointly with others, shall belong solely to the Company,
                  whether or not they are protected or protectable under
                  applicable patent, trademark, service mark, copyright or trade
                  secret laws.

         3.3      ASSIGNMENT OF RIGHTS. The Employee hereby assigns and agrees
                  to assign to the Company or its designee, all of the
                  Employee's right to and title and interest in all Inventions
                  and Other Intellectual Property, made or created during the
                  Employee's period of employment with the Company, and to
                  applications for United States and foreign letters patent and
                  United States and foreign letters patent granted upon such
                  Inventions and to all maskworks, copyrightable materials,
                  trademark materials, and materials related thereto made or
                  created during the Employee's period of employment with the
                  Company.

         3.4      ASSIGNMENT OF COPYRIGHTS. To the extent that any work is not
                  assigned by provision of PARAGRAPHS 3.2 and 3.3 of this
                  Agreement, all work by the Employee under the Agreement,
                  regardless of where or when the work is performed, is deemed
                  to be a "work made for hire" to which copyright vests with the
                  Company. To the extent any work performed by the Employee
                  under this Agreement is not a "work made for hire," the
                  Employee hereby assigns and transfers, and agrees to assign
                  and transfer, the Employee's copyright in the work to the
                  Company.

         3.5      DUTY TO COOPERATE. The Employee agrees for himself and the
                  Employee's heirs, personal representatives, successors and
                  assigns, upon request of the Company, to at all times during
                  and after employment, perform all acts that are reasonable and
                  deemed necessary or desirable by the Company to secure the
                  full benefits, enjoyment, rights and title to the Inventions
                  or Other Intellectual Property and otherwise to carry into
                  full force and effect the text and the intent of the
                  assignment agreement set out in PARAGRAPHS 3.2, 3.3 and 3.4
                  preceding, including but not limited to giving testimony in
                  support of the Employee's inventorship, and to execute and
                  deliver promptly to the Company such papers, instruments and
                  documents without expense to the Employee, as from time to
                  time may be necessary or useful in the Company's opinion to
                  apply for, secure, enforce, maintain, reissue or defend the
                  Company's or its designee's worldwide rights in the Inventions
                  and Other Intellectual Property made or created during the
                  Employee's period of employment with the Company or in any or
                  all United States letters patent and in any and all letters
                  patent in any country foreign to the United States. This
                  obligation shall survive the term and termination of this
                  Agreement. Employee shall be compensated by the Company at
                  reasonable rates for time in complying with this provision
                  after his termination from Employment.

         3.6      NO VIOLATION OF THIRD PARTY AGREEMENTS OR POLICIES. The
                  Employee warrants and represents to the Company that she or he
                  is not subject to any agreement or company or university
                  policy inconsistent with the Agreement regarding Inventions
                  and Other Intellectual Property set forth herein.

         3.7      ATTORNEY-IN-FACT. In the event that the Company is unable for
                  any reason to secure the Employee's signature on any document
                  required to apply for or execute any patent, copyright, mask
                  work or other applications with respect to any Inventions and
                  Other Intellectual Property rights (including improvements,
                  renewals, extensions, continuations, decisions or
                  continuations-in-part thereof), the Employee hereby
                  irrevocably designates and appoints the Company and its duly
                  authorized officers and agents as his/her agents and
                  attorneys-in-fact to act on his/her behalf and instead of
                  Employee, to execute and file any such application


                                       2

<PAGE>

                  and to do all other lawfully permitted acts to further the
                  prosecution and issuance of patents, copyrights, mask works or
                  other rights made or created during the Employee's period of
                  Employment with the Company thereon with the same legal force
                  and effects as if executed by the Employee.



SECTION 4.        SHOP RIGHT.

         Notwithstanding any provision of this Agreement creating greater
rights, the Company shall have the royalty-free worldwide right to use in its
business, and to make, have made, use, sell, offer for sale, or import products,
processes and services derived from, any inventions, discoveries, concepts and
ideas, whether or not patentable, including but not limited to systems, devices,
software, processes, methods, formulae, and techniques, as well as improvements
thereof and know-how related thereto, that are not Inventions as defined herein,
but which are made or conceived by the Employee during the Employee's engagement
by the Company or associated companies or with the use or assistance of the
Company's Facilities, Materials or Personnel to the extent permitted by
applicable federal and state law.

SECTION 5.        CONFIDENTIALITY

         5.1      DEFINITIONS. As used in this Agreement, the term "CONFIDENTIAL
                  AND PROPRIETARY INFORMATION" means Company trade secrets, as
                  well as any and all information disclosed to or known by the
                  Employee as a consequence of or through the Employee's
                  engagement by the Company or associated companies or
                  employees, or which the Employee has assigned or is under an
                  obligation to assign to the Company, about the Company's
                  plans, products, processes and services, including, without
                  limitation, (a) information of a technical nature, such as
                  information regarding past, present and future research,
                  discoveries, ideas, concepts, know-how, techniques, designs,
                  specifications, drawings, blueprints, tracings, diagrams,
                  models, samples, data, product information, marketing plans,
                  computer programs (whether in source or object code form or
                  other form and whether contained on program listings, magnetic
                  tape, magnetic disks, CD ROMs or other media), computer
                  program documentation, disks, diskettes, tapes, logic, flow
                  charts, specifications, documentation and ideas relating to
                  the activities of the Company, (b) information of a business
                  nature, such as information regarding past, present and future
                  client development, financial data, prospective and actual
                  customer names, lists, or proposals, patent applications,
                  business information, strategic and development plans,
                  employee lists, business manuals, marketing plans, strategies,
                  procurement specifications, contacts, quotations, and (c) all
                  documents, drawings, reports, client lists, and other physical
                  embodiments of all such information.

         5.2      Except as specifically directed or consented to by the Company
                  in writing, the Employee will not, directly or indirectly,
                  during or after the term of the Employee's engagement by the
                  Company, communicate, disclose, or cause to have communicated
                  or disclosed, in any way, any trade secrets of the Company or
                  other Confidential and Proprietary Information. Nothing
                  contained herein shall prevent Employee from disclosing trade
                  secrets or Confidential and Proprietary Information if so
                  directed by a court of competent jurisdiction or to her or his
                  legal advisors and others with a legitimate reason to know as
                  part of any legal proceedings or dispute concerning such
                  Information.

         5.3      The restriction of PARAGRAPH 5.2 shall not apply to
                  information that the Employee can establish, by competent
                  proof: (i) was known, other than under binder of secrecy, to
                  the Employee prior to the Employee's engagement by the
                  Company; (ii) has passed into the public domain prior to or
                  after its development by or for the Company other than through
                  acts or omissions attributable to the Employee; or (iii) was
                  subsequently obtained other than under binder of secrecy from
                  a third party other than the Company or associated companies.

         5.4      Upon termination of the Employee's engagement by the Company,
                  or at any other time upon the request of the Company, the
                  Employee shall forthwith deliver to the Company any and all
                  documents, notes, notebooks, letters, manuals, prints,
                  drawings, block diagrams, photocopies of documents, devices,
                  hardware, data, databases, source code, object code, and data
                  or computer programming code stored on an optical or
                  electronic medium, relating to the Company's business and
                  affairs, including all materials that are in the possession of
                  or under the control of the Employee and that incorporate any
                  Confidential and Proprietary Information or any reference
                  thereto.

         5.5      The Employee acknowledges that the Company's Confidential and
                  Proprietary Information constitutes unique and valuable assets
                  of the Company, the loss or unauthorized disclosure of which
                  would cause the Company irreparable harm. Upon the breach or
                  threatened breach by the Employee of any of the provisions of
                  this SECTION 5, the Company shall be entitled to an
                  injunction, without bond, restraining the Employee from
                  committing such breach. This right to an injunction shall not
                  be construed to prohibit the Company from pursuing any other
                  remedies available to it at law or in equity for such breach
                  or threatened breach, including the recovery of damages. In
                  case of any dispute hereunder, the parties will submit to the
                  jurisdiction and venue of any court of competent jurisdiction,
                  including such courts in Suffolk County, Massachusetts, and
                  will comply with all requirements necessary to give such court
                  jurisdiction over the parties and the controversy. EACH PARTY
                  HEREBY WAIVES ANY RIGHT TO A JURY TRIAL AND TO CLAIM OR
                  RECOVER PUNITIVE DAMAGES.


                                       3

<PAGE>

The Employee acknowledges that the Company's Confidential and Proprietary
Information constitutes unique and valuable assets of the Company, the loss or
unauthorized disclosure of which would cause the Company irreparable harm. Upon
the breach or threatened breach by the Employee of any of the provisions of this
SECTION 5, the Company shall be entitled to an injunction, without bond,
restraining the Employee from committing such breach. This right to an
injunction shall not be construed to prohibit the Company from pursuing any
other remedies available to it at law or in equity for such breach or threatened
breach, including the recovery of damages. In case of any dispute hereunder, the
parties will submit to the jurisdiction and venue of any court of competent
jurisdiction, and will comply with all requirements necessary to give such court
jurisdiction over the parties and the controversy. EACH PARTY HEREBY WAIVES ANY
RIGHT TO A JURY TRIAL AND TO CLAIM OR RECOVER PUNITIVE DAMAGES.

SECTION 6.        COVENANT NOT TO COMPETE

         6.1      DEFINITIONS. As used in this Agreement, the term "COMPETING
                  ORGANIZATION" means any person or organization engaged in or
                  with specific plans to become engaged in research on, or
                  development, production, marketing or selling of a Competing
                  Product, and the term "COMPETING PRODUCT" means any product,
                  process or service of any person or organization other than
                  the Company, whether or not in existence, that competes or is
                  likely to compete, directly or indirectly, with a product,
                  process or service that is being developed, sold or marketed
                  at the time the Company seeks to enforce this paragraph and
                  upon or with which the Employee has worked for the Company or
                  about which the Employee acquired Confidential and Proprietary
                  Information by virtue of engagement with the Company.

         6.2      The Employee agrees and acknowledges that in order to assure
                  the Company that it will retain its value as a going concern,
                  it is necessary that the Employee undertake not to utilize the
                  Employee's special knowledge of the technology and the
                  business of the Company and the Employee's relationships with
                  customers and suppliers to compete with the Company. Employee
                  further acknowledges that:

              i.      The Employee occupies a position of trust and confidence
                      with the Company and, during Employee's engagement under
                      this Agreement, the Employee will become familiar with the
                      Company's trade secrets and with other Confidential and
                      Proprietary Information;

              ii.     The agreements and covenants contained in this Section 6
                      are essential to protect the Company and its associated
                      goodwill; and

              iii.    The Employee's engagement with the Company has special,
                      unique and extraordinary value to the Company, and the
                      Company would be irreparably damaged if the Employee were
                      to provide services to any person or entity in violation
                      of the provisions of this Agreement.

         6.3      During the term of this Agreement and for a period of one year
                  thereafter, the Employee will not render services, directly or
                  indirectly, to any Competing Organization which is engaged in
                  marketing or selling of a Competing Product in the United
                  States, except that the Employee may accept employment with,
                  or render services to, (i) a Competing Organization whose
                  business is diversified, but only to the parts of such
                  business which are not a Competing Organization, provided that
                  the Company, prior to the Employee's accepting such employment
                  or rendering such services, shall receive separate written
                  assurance satisfactory to the Company from such Competing
                  Organization and from the Employee that the Employee will not
                  render services directly or indirectly in connection with any
                  Competing Product or (ii) any university or academic
                  institution


                                       4

<PAGE>

                  so long as such employment or engagement does not involve use
                  or disclosure of any Confidential and Proprietary Information
                  or research on or development of any Competing Product.
                  Nothing contained herein shall preclude Employee from
                  participating, directly or indirectly, as a passive investor
                  in the securities of any publicly-traded corporation. The
                  Employee agrees to disclose to every Competing Organization,
                  by which the Employee may subsequently be employed or engaged,
                  the restrictions upon the Employee's services herein
                  contained.

         6.4      During the Employee's engagement by the Company and for a
                  period of one year after the Employee ceases to be engaged by
                  the Company, the Employee shall not, directly or indirectly,
                  solicit as employees, partners, or in any other personal or
                  representative capacity any present employee of the Company
                  for the purpose of securing business or contracts related to
                  the business in which Company is engaged, or competing with
                  Company.

         6.5      During Employee's engagement by the Company and for a period
                  of one year after Employee ceases to be engaged by Company,
                  the Employee shall not, directly or indirectly, solicit
                  business from, divert business from, or attempt to convert to
                  other methods of using the same or similar products or
                  services as provided by Company, any existing client, account
                  or location of Company at the time of any such solicitation or
                  attempted diversion with which the Employee has had any
                  contact as a result of the Employee's engagement by Company.

         6.6      If any court of competent jurisdiction shall at any time deem
                  the term of this Agreement or any particular restrictive
                  covenant too lengthy or the territory too extensive, the other
                  provisions of this Section 6 shall nevertheless stand, the
                  restricted period shall be deemed to be the longest period
                  permissible by law under the circumstances and the territory
                  shall be deemed to comprise the largest territory permissible
                  by law under the circumstances. The court in each case shall
                  reduce the restricted period and/or territory to permissible
                  duration or size.

         6.7      The Employee will not assert any rights under any Inventions
                  and Other Intellectual Property, discoveries, concepts or
                  ideas or improvements thereof or know-how related thereto, as
                  having been made or acquired by the Employee prior to the
                  Employee's engagement by the Company except as disclosed in
                  writing in EXHIBIT A to this Agreement. The Employee
                  represents that the list in EXHIBIT A is complete. If there is
                  no such list on EXHIBIT A, the Employee represents that the
                  Employee has no rights in any such Inventions and Other
                  Intellectual Property, discoveries, concepts or ideas or
                  improvements thereof or know-how related thereto.

SECTION 7.        GENERAL PROVISIONS.

         7.1      BINDING EFFECT. This Agreement shall be binding upon and inure
                  to the benefit of the parties hereto and their respective
                  heirs, personal representatives, successors, and assigns.

         7.2      COUNTERPARTS. This Agreement may be executed simultaneously in
                  any number of counterparts, each of which shall be deemed an
                  original but all of which together shall constitute one and
                  the same instrument.

         7.3      PRESUMPTION. This Agreement or any section thereof shall not
                  be construed against any party due to the fact that this
                  Agreement or any section hereof was drafted by such party.

         7.4      GOVERNING LAW. This Agreement, and all transactions
                  contemplated hereby, shall be governed by, construed, and
                  enforced in accordance with the laws of the Commonwealth of
                  Massachusetts, without reference to the conflict of laws
                  provisions thereof.

         7.5      SEVERABILITY. If any term, provision, clause, article,
                  condition or other portion of this Agreement is determined to
                  be invalid, void, or unenforceable by a court of competent
                  jurisdiction, the same will be deemed amended or deleted to
                  the extent necessary to make it enforceable, and it will not
                  affect any other term, provision, clause, article, condition,
                  or other portion hereof, and the remainder of this Agreement
                  will remain in full force and effect.

         7.6      NO CONFLICT. The Employee warrants and represents to the
                  Company that the Employee is not now under any obligation of a
                  contractual or other nature to any person, firm, corporation,
                  or university which is inconsistent


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<PAGE>

                  or in conflict with this Agreement or any provision hereof, or
                  which would prevent, limit or impair in any way the execution
                  of this Agreement or the performance by the Employee's
                  obligations hereunder, and the Employee will indemnify and
                  hold harmless the Company, its directors, officers and
                  employees against and in respect of all liability, loss,
                  damage, expense, or deficiency resulting from any
                  misrepresentation, or breach of any warranty or agreement made
                  by Employee in connection with Employee's employment
                  hereunder.

         7.7      NOTICES. All notices or other communications required or
                  permitted by this Agreement to be given or made by one party
                  to the other shall be made or given in writing and delivered
                  either in person, by overnight delivery, by certified mail or
                  registered mail, postage prepaid, return receipt requested or
                  by telex or facsimile to the Company at the address specified
                  below, or to the Employee at the address maintained in the
                  Company's records, which Employee agrees to keep up to date.
                  Such notice will be effective upon delivery or transmission in
                  such a manner. Proof of delivery or transmission in such a
                  manner shall constitute proof of receipt.


                           iBasis, Inc.
                           ATTN: Ms. Tamah Rosker
                           20 Second Avenue
                           Burlington, MA 01803
                           FAX:  (781) 505-7330

         7.8      SURVIVAL OF OBLIGATIONS. Sections 3, 4, 5, and 6 of this
                  Agreement, including the Employee's obligations to the Company
                  regarding Confidential and Proprietary Information and the
                  Employee's covenant not to compete with the Company as set for
                  the herein, shall survive the term and termination of this
                  Agreement.

         7.9      ENTIRE AGREEMENT. This Agreement sets forth the entire
                  agreement of the parties hereto in respect of the subject
                  matter contained herein and supersedes all prior agreements,
                  promises, covenants, arrangements, communications,
                  representations or warranties, whether oral or written, by any
                  officer, employee or representative of any party hereto in
                  respect of such subject matter. Any prior agreement of the
                  parties hereto in respect of the subject matter contained
                  herein is hereby terminated and canceled.

         7.10     AGREEMENT READ. UNDERSTOOD AND FAIR. Employee has carefully
                  read and considered all provisions of this Agreement and
                  agrees that all of the restrictions set forth are fair and
                  reasonable and are reasonably required for the protection of
                  the interests of Company.

         7.11     WAIVER. None of the provisions of this Agreement shall be
                  deemed to be waived by any act or acquiescence on the part of
                  the company or its agents. No waiver of any provision of this
                  Agreement shall constitute a waiver of any other provision.
                  The failure of the Company to enforce a provision of this
                  Agreement shall not be deemed a waiver of that provision.

         7.12     PROOF OF LEGAL AUTHORITY. Under federal immigration laws, the
                  Company is required to verify each new employee's identity and
                  legal authority to work in the United States. Therefore, the
                  Employee's employment pursuant to this Agreement is contingent
                  upon the Employee submitting the legally required proof of the
                  Employee's identity and authorization to work in the United
                  States. Not later than the Employee's third day of employment,
                  the Employee will provide the required identification.

         7.13     Except as provided above in Paragraph 5.5 and except for
                  claims arising out of the Workers Compensation Act, either
                  party may require that all disputes or injuries arising out of
                  the employment relationship between the Employee and the
                  Company, including but not limited to claims for breach of
                  contract; wrongful termination; age, sex, race or other
                  unlawful discrimination or harassment; defamation; violation
                  of public policy; and any dispute over the validity of, breach
                  or rescission of this Agreement, shall be settled by an
                  arbitration in accordance with the commercial arbitration
                  rules of the American Arbitration Association before a one (1)
                  person panel. The English language shall be used throughout
                  the arbitral proceeding. The arbitration shall take place in
                  Boston, Massachusetts, U.S.A. The cost of the arbitration,
                  including the fees and expenses of the arbitrator(s), shall be
                  shared equally by the Parties unless that award provides
                  otherwise. Any decision or order of the arbitrator shall be
                  binding upon the parties hereto. Judgment upon any award so


                                       6

<PAGE>

                  rendered may be entered in any court having jurisdiction.
                  Except as provided above in PARAGRAPH 5.5 above, the Employee
                  and the Company agree that arbitration is the sole and
                  exclusive remedy, and each party waives the right to a jury
                  trial and to seek legal relief in any other forum. This
                  provision however, shall not prohibit the Employee or the
                  Company from obtaining injunctive relief pending arbitration.

         I UNDERSTAND THAT THIS AGREEMENT AFFECTS MY RIGHTS TO INVENTIONS I MAKE
DURING MY EMPLOYMENT, AND RESTRICTS MY RIGHTS TO DISCLOSE OR USE THE COMPANY'S
CONFIDENTIAL INFORMATION OR TO COMPETE WITH THE COMPANY DURING OR SUBSEQUENT TO
MY EMPLOYMENT.

         I HAVE READ THIS AGREEMENT CAREFULLY AND UNDERSTAND ITS TERMS. I HAVE
COMPLETELY FILLED OUT EXHIBIT A TO THIS AGREEMENT.

Dated: SEPT. 20, 2001.

                                       /s/ Richard G. Tennant
                                       Signature


                                       Richard G. Tennant
                                       Name of Employee


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

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

                                       ---------------------------------
                                       Address



ACCEPTED AND AGREED:

iBASIS, INC.


By:      /S/ T. ROSKER
   -----------------------------------------
          Signature

         T. ROSKER
   -----------------------------------------
           Print

Title:   VP HR
      --------------------------------------


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