Document:

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                                                                   EXHIBIT 10.11

                             Arbinet Holdings, Inc.
                           33 Whitehall St, 19th floor
                                  New York, NY

                                                                March 29th, 2000

Mr J. Curt Hockemeier
3 Peacan Valley Court
Skillman, NJ 08558
Tel#: (609) 466-1260

Dear Curt,

On behalf of Arbinet Holdings, Inc. (the "Company"), I am pleased to extend to
you an offer of employment in accordance with the following terms:

     1.   Title and Position. Effective immediately following your acceptance of
          this offer you will serve as an executive of the Company, initially as
          President and Chief Operating Officer of the Company. After an initial
          period, not to exceed year end, December 31, 2000, you will be
          appointed to the position of Chief Executive Officer. You will report
          to the Chief Executive Officer and Chairman of the Board of Directors
          of the Company until your appointment as Chief Executive Officer;
          thereafter, you will report to the Board of Directors.

     2.   Duties and Obligations. During your employment, you will devote your
          full business time, interest and effort to the performance of your
          duties with the Company. You will have during the initial period as
          President and COO, all of the functions of the Company reporting to
          you other than the Founder, Finance, Business Development and Legal.
          Subsequent to your appointment as Chief Executive Officer, these
          functions will also report to you.

     3.   Employment Relationship. Should you decide to accept the Company's
          offer, your employment will be "at-will" and your employment may be
          terminated by either you or the Company at any time for any reason (or
          no reason), by providing sixty (60) days prior written notice to the
          other party. Further, your participation in any Company benefit or
          equity program does not constitute an agreement by the Company to
          employ or continue to employ you for any period of time.

     4.   Salary. While you are employed on a full-time basis by the Company,
          the Company will pay you abase salary, which annualizes to $300,000,
          payable in accordance with the usual payroll practices of the Company
          including the withholding of all income and

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J. Curt Hockemeier - Offer Letter
March 29, 2000
Page 2 of 5

          employment taxes. You will receive a one time "sign-on" bonus of
          $200,000 upon commencement of employment, payable pursuant to your
          instructions. At the time of your appointment as Chief Executive
          Officer, your salary will be increased to $400,000 annually.
          Thereafter, your base salary will be reviewed by the Compensation
          Committee of the Board of Directors on an annual basis and may be
          subject to adjustment upward based on various factors including,
          without limitation, your performance and the Company's achievement of
          its business plan (as determined by the Board of Directors).

     5.   Equity.

          (a)  The Board of Directors (or a duly authorized committee thereof)
               will grant to you, in the form of stock options ("Options"), the
               right to purchase 1,200,000 shares of Common Stock of the
               Company, at the lowest available employee plan price as of the
               acceptance of this offer (the current employee plan exercise
               price as approved by the Board of Directors on March 12th, 1999
               is approximately $5.71), subject to minor adjustments to the
               capitalization table and the following vesting schedule: such
               Options will become exercisable as to l/48th of the Options on
               the last day of each full month you are employed by the Company
               (the "Vesting Dates"), provided you are employed by the Company
               on the applicable Vesting Dates. To the maximum extent
               permissible, these will be incentive stock option as defined by
               the Internal Revenue Code of 1986, as amended (the "Code"), and
               the Arbinet Holdings, Inc. 1997 Stock Incentive Plan (the "Stock
               Plan").

          (b)  At your option, you will be provided with a loan to acquire the
               Option shares at the current option price. The vesting schedule
               will be replaced by an agreement for the Company to repurchase
               the unvested shares at the exercise price. This agreement for
               repurchase will expire as to the option to repurchase at the rate
               of 1/48th of the shares per month. In the event you elect this
               option, the original Option shares will be vested co-incident
               with the execution of the loan agreement and repurchase option
               granted by you to the Company to permit your immediate purchase.

          (c)  Except as otherwise provided in the Stock Plan and Section 7
               below, you shall forfeit to the Company (without compensation)
               all unvested Options on the date your employment with the Company
               terminates.

          (d)  If you have not been appointed as Chief Executive Officer, then
               in the event of termination of your employment by the Company in
               the 12 months following a change of control of more than 50% of
               the Company's voting stock, other than an IPO (a "Change of
               Control"), all unvested options will accelerate, and become
               exercisable or, alternatively, all repurchase rights will expire
               (collectively, the "Acceleration"). If you have been appointed as
               Chief Executive Officer, then Acceleration will occur upon a
               Change of Control.

          (e)  Following a termination of employment you will have six (6)
               months to exercise all vested options unless a longer period is
               provided in the stock option plan or agreement.

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J. Curt Hockemeier - Offer Letter

March 29, 2000
Page 3 of 5

     6.   Benefits. You will participate, to the extent you are eligible and
          subject to confirming coverage with the applicable underwriter (if
          any), in all of the Company's employee benefit programs generally
          provided to the other executive officers, in accordance with the terms
          thereof as in effect from time to time; provided that your annual
          vacation shall not exceed 4 weeks.

     7.   Termination of Employment.

          (a)  In the event your employment hereunder is terminated by the
               Company without cause or by you for Good Reason (as defined
               below), the Company will pay you, subject to your compliance with
               Sections 8 and 9 below, (i) any unpaid base salary through the
               date of termination and any accrued vacation pay; (ii) severance
               pay equal to twelve (12) months' base salary at the rate in
               effect on the date of termination; (iii) an amount reimbursing
               you for the applicable premium payment for any COBRA coverage
               payable under a Company health or welfare plan for you and your
               dependents during the twelve (12) month period following the date
               of termination (the "Twelve Month Period"); and (iv) an amount
               equal to any employer contribution that would have been made by
               the Company to any retirement plan of the Company on your behalf
               had you remained employed by the Company during the Twelve Month
               Period assuming you contributed the maximum amount to such plan.
               Notwithstanding the foregoing, the amounts paid to you pursuant
               to subsections (iii) and (iv) of this Section 7(a) shall not
               exceed $25,000. In addition, if your employment is terminated by
               the Company without cause or by you for Good Reason under the
               provisions this Section 7, you will be granted accelerated
               vesting of 16/48ths of the option share grant, or accelerated
               expiration of 16/48ths of the repurchase rights whichever is
               applicable.

          (b)  In the event your employment hereunder is terminated for any
               other reason, the Company will pay you any unpaid base salary and
               compensation for accrued vacation through the date of
               termination.

     In addition, in all termination events, except as specifically provided in
     Section 5 hereof, the Company will pay you any other amounts or benefits
     owing to you under the then applicable employee benefit plans and programs
     of the Company in accordance with such plans and programs. For purposes of
     this letter "cause" shall mean any of the following: (w) your willful
     misconduct in the performance of your duties to the Company, or your
     willful failure to implement any legal policy of the Company, (x)
     conviction of or plea of guilty or any other plea other than "not guilty"
     to a felony; (y) the violation by you of any material provision of this
     letter which either is not cured within ten days after a written notice is
     given to you by the Company or constitutes a habitual breach; or (z) your
     dishonesty, misappropriation or fraud with regard to the property of the
     Company or its affiliates.

     You may terminate your employment for Good Reason. "Good Reason" means,
     without your written consent: (i) a material adverse change in your title
     or the duties assigned to you; (ii) any material failure by the Company to
     comply with the provisions of this Agreement; or (iii) any requirement by
     the Company that your primary office location be other than in the states
     of New York, New Jersey or Connecticut.

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J. Curt Hockemeier - Offer Letter
March 29, 2000
Page 4 of 5

     8.   Confidential Information. While providing your services, you will have
          access to and will obtain confidential information as to the Company,
          its affiliates, its employees and its customers and you may during the
          course of your employment develop certain information, inventions or
          other intellectual property. As a condition of your employment with
          the Company, you will be required to enter into the Company's Employee
          Inventions and Confidentiality Agreement (the "Confidentiality
          Agreement") The Confidentiality Agreement exists to assure the Company
          and its investors that the Company's valuable intellectual property
          and its rights thereto are protected.

     9.   Non-Competition/Non-Solicitation. (a) You agree that during your
          employment and for a period following the date your employment
          terminates of (i) two (2) years if your employment is terminated by
          the Company for cause or by you without Good Reason or (ii) one (1)
          year if your employment is terminated for any other reason, as the
          case may be, (the "Restricted Period"), you will not enter into
          Competition with the Company. "Competition" shall mean participating,
          directly or indirectly, as an individual proprietor, partner,
          stockholder, officer, employee, director, joint venturer, investor,
          lender, consultant or in any capacity whatsoever in a business in
          competition with any business conducted by the Company or its
          affiliates (a "Competitor") in any jurisdiction where the Company
          and/or its affiliates conduct as of the date your employment
          terminates such business, which shall be deemed to include, without
          limitation, any business activity or j jurisdiction which is covered
          by or included in a written proposal of business plan existing on the
          date of the termination; provided, however, that such participation
          shall not include (i) the mere ownership of not more than one percent
          (1%) of the total outstanding stock of a publicly-held company; (ii)
          the performance of services for any enterprise to the extent such
          services are not performed, directly or indirectly, for a business
          unit of the enterprise in the aforesaid Competition; or (iii) any
          activity engaged in with the prior written approval of the Board.

          (a)  You agree that, during the Restricted Period, you will not,
               directly or indirectly (i) solicit, recruit or hire any
               non-administrative or non-clerical employee of the Company for
               the purpose of being employed by you or by any Competitor of the
               Company on whose behalf you are acting as an agent,
               representative or employee and that you will not convey any
               confidential information or trade secrets about other employees
               of the Company to any other person or (ii) influence or attempt
               to influence customers or suppliers of the Company or its
               affiliates to direct their business to any Competitor of the
               Company.

          (b)  You acknowledge that Sections 8 and 9 above are reasonable and
               necessary for the protection of the business of the Company and
               its affiliates and that part of the compensation to be paid under
               this letter is in consideration for the provisions contained in
               Sections 8 and 9. If any restriction set forth with regard to
               competition or solicitation of employees or customers is found by
               any court of competent jurisdiction to be unenforceable because
               it extends for too long a period of time or over too great a
               range of activities or over too broad a geographic area, it shall
               be interpreted to extend over a maximum period of time, range of
               activities or geographic area as to which it may be enforceable.
               You further acknowledge and consent that the Company would by
               reason of such

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J. Curt Hockemeier - Offer Letter
March 29, 2000
Page 5 of 5

               competition or solicitation of employees or customers be entitled
               to injunctive relief in a court of appropriate jurisdiction
               prohibiting you from competing with the Company or its affiliates
               or engaging in solicitation in violation of this letter.

     10.  Governing Law/Miscellaneous. This letter is subject to the laws of the
          State of New York. This letter, along with the Confidentiality
          Agreement, sets forth the terms of your employment with the Company
          and supercedes all prior agreements, arrangements and communications,
          whether oral or written, between the Company and you. This letter may
          not be altered, modified, or amended except by written instrument
          signed by an individual authorized to sign of behalf of the Company
          (other than you) and by you. This letter may not be assigned in whole
          or in part, except that the Company may assign it to an acquiror of
          all or substantially all of the assets of the Company. This letter
          shall be binding on the successors and permitted assignees of the
          parties hereto. Except with regard to disputes arising under Section 8
          or 9 hereof, any dispute arising hereunder will be submitted to a
          neutral arbitrator selected by the parties. Such arbitrator shall
          conduct such arbitration in New York City under the rules of the
          American Arbitration Association. The Company will reimburse you for
          reasonable fees and expenses incurred by you in conjunction with this
          offer letter, up to $5,000.

This offer is made to you based on your representation to the Company that your
acceptance of employment with the Company and performance of the contemplated
services does not and will not conflict with or result in any breach or default
under, any agreement, contract or arrangement to which you are a party or
violate any other legal restriction. If you find this offer of employment
acceptable, please sign the enclosed copy of this letter and return it to us.

                                         Very truly yours,

                                         Arbiner Holdings, Inc.

                                         By: /s/ Anthony L. Craig
                                             -----------------------------------
                                         Name: Anthony L. Craig
                                         Title: Chairman and Chief Executive
                                                Officer

Agreed and Accepted:

/s/ J. Curt Hockemeier
-----------------------------------------
J. Curt Hockemeier

Dated: April 4, 2000<PAGE>
                                                                   EXHIBIT 10.12

July 5, 2001

Mr. Peter P. Sach
5333 Pinyon Jay Road
Parker, CO 80134-2722

Dear Peter:

On behalf of Arbinet-thexchange, Inc. (the "Company"), I am pleased to extend to
you an offer of employment in accordance with the following terms:

Title: You will serve as Senior Vice President and Chief Administrative Officer
(CAO). You will report to the President and CEO and based in New York, NY.

Duties and Obligations: During your employment you will devote your full
business time, interest and effort to the performance of your duties with the
Company. These duties include those which are commonly associated with the Chief
Financial Officer position, and additionally will include management and
oversight of the Company's information technology (I.T.) initiatives and the
human resources function.

Employment Relationship: Your employment will be "at-will" and may be terminated
by either you or the Company at any time for any reason or no reason, by
providing sixty (60) days written notice to the other party. Further, your
participation in any Company benefit or equity program does not constitute an
agreement by the Company to employ or continue to employ you for any period of
time.

Salary and Bonus: While you are employed on a full-time basis by the Company,
the Company will pay you a base salary which annualizes to $250,000, payable in
accordance with the usual payroll practices of the Company including the
withholding of all income and employment taxes. Your base salary will be
reviewed on an annual basis and may be subject to adjustment upward based on
various factors including, without limitation, your performance or the Company's
achievement of its business plan (as determined by the Board of Directors of the
Company), provided that in no event shall such annual increase be less than the
annual rate of increase in the Consumer Price Index. When the Company completes
an Initial Public Offering (IPO) your annualized salary will be increased to
$275,000. You will be eligible for a 40% target bonus based upon achievement of
assigned performance goals and subject to the approval of the Board of
Directors.

Relocation: Per the attached.

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Relocation Expense Repayment: In the event you do not complete 12 months of
service following the payment of the Relocation payments, the Company will be
entitled to repayment of the full amount, less an allowance pro rata to the
months served (e.g., if you serve five months after the Relocation payments, you
will be required to repay 7/12 of such payments).

Equity: The Board (or duly authorized committee thereof) will grant to you, in
the form of stock options ("Options"), the right to purchase shares of Common
Stock of the Company which equal 3/4 of 1% of the Company immediately following
the closing of the Series E round of investment. This grant will be at the
lowest available employee plan price as of the acceptance of this offer, subject
to the following vesting schedule: such Options will become exercisable as to
1/48th each month as long as you are employed by the Company; provided, further,
that in the event of termination of employment without cause in the 12 months
following a "change of control" event (which will not include an IPO or a
private equity financing transaction), any remaining unvested options will then
vest.

Benefits: You will participate, to the extent eligible and subject to confirming
coverage with applicable underwriters (if any), in all of the Company's employee
benefit programs generally provided to the other executive officers, in
accordance with the terms thereof as in effect from time to time; provided that
your annual vacation shall not exceed four (4) weeks.

Termination of Employment:

     a.   In the event your employment hereunder is terminated by the Company
          without cause, the Company will pay you, subject to your compliance
          with this and paragraphs b, c and d following, (i) any unpaid base
          salary through the date of termination and any accrued vacation; (ii)
          severance pay equal to twelve (12) month's base salary at the rate in
          effect on the date of termination; (iii) an amount reimbursing you for
          the applicable premium payment for any COBRA coverage payable under a
          Company health or welfare plan for you and your dependents during the
          12 month period following the date of termination (the "Twelve Month
          Period"); and (iv) an amount equal to any employer contribution that
          would have been made by the Company pursuant to any retirement plan of
          the Company on your behalf and you remained employed by the Company
          during the Twelve Month Period assuming you contributed the maximum
          amount to such plan. Notwithstanding the foregoing, the amounts paid
          to you pursuant to subsections (iii) and (iv) of this paragraph (a)
          shall not exceed $25,000.

     b.   In the event your employment hereunder is terminated for any other
          reason, the Company will pay you any unpaid base salary and
          compensation for accrued vacation through the date of termination.

<PAGE>

     c.   In addition, in all termination events, except as specifically
          provided in the Relocation Expense Repayment section, the Company will
          pay you any other amounts or benefits owing to you under the then
          applicable employee benefit plans and programs of the Company in
          accordance with such plans and programs.

     d.   For purposes of this letter, "cause" shall mean any of the following:
          (w) your willful misconduct in the performance of your duties to the
          Company, or your willful failure to implement any legal policy of the
          Company, (x) conviction of or plea of guilty or any plea other than
          "not guilty" to a felony; (y) the violation by you of any material
          provision of this letter which either is not cured within ten days
          after a written notice is given to you by the Company or constitutes a
          habitual breach; or (z) your dishonesty, misappropriation of fraud
          with regard to the property of the Company or its affiliates.

Confidential Information: While providing your services, you will have access to
and will obtain confidential information as to the Company, its affiliates, its
employees and its customers and you may during the course of your employment
develop certain information, inventions or other intellectual property. As a
condition of your employment with the Company, you will be required to enter
into the Company's Employee Inventions and Confidentiality Agreement (the
"Confidentiality Agreement"). The Confidentiality Agreement exists to assure the
Company and its investors that the Company's valuable intellectual property and
its rights thereto are protected.

Non-Competition/Non-Solicitation:

     a.   You agree that during your employment term hereunder and for a twelve
          month period following the date your employment terminates, you will
          not enter into Competition with the Company. "Competition" shall mean
          participating, directly or indirectly, as an individual proprietor,
          partner, stockholder, officer, employee, director, joint venturer,
          investor, lender, consultant or in any capacity whatsoever in a
          business in competition with any business conducted by the Company or
          its affiliates (a "Competitor") in any jurisdiction where the Company
          and/or its affiliates conduct as of the date your employment
          terminates such business, which shall be deemed to include, without
          limitation, any business activity or jurisdiction which is covered by
          or included in a written proposal or business plan existing on the
          date of the termination of the employment term hereunder; provided
          however, that such participation shall not include (i) the mere
          ownership of not more than one percent (1%) of the total outstanding
          stock of a publicly held company; (ii) the performance of services for
          any enterprise to the extent such services are not performed, directly
          or indirectly, for a business unit of the enterprise in the aforesaid
          Competition; or (iii) any activity engaged in with the prior written
          approval of the Board.
     b.   You agree that, during the one (1) year period following the date your
          employment terminates, you will not, directly or indirectly (i)
          solicit, recruit

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          or hire any non-administrative or non-clerical employee of the Company
          for the purpose of being employed by you or by any Competitor of the
          Company on whose behalf you are acting as an agent, representative or
          employee and that you will not convey any confidential information or
          trade secrets about other employees of the Company to any other person
          or (ii) influence or attempt to influence customers or suppliers of
          the Company or its affiliates to direct their business to any
          Competitor of the Company
     c.   You acknowledge that the foregoing are reasonable and necessary for
          the protection of the business of the Company and its affiliates and
          that part of the compensation paid under this letter is in
          consideration for these provisions. If any restrictions set forth with
          regard to competition or solicitation of employees or customers is
          found by any court of competent jurisdiction to be unenforceable
          because it extends for too long a period of time or over too great a
          range of activities or over too broad a geographic area, it shall be
          interpreted to extend over a maximum period of time, range of
          activities or geographic area as to which it may be enforceable. You
          further acknowledge and consent that the Company would by reason of
          such competition or solicitation of employees or customers be entitled
          to injunctive relief in a court of appropriate jurisdiction
          prohibiting you from competing with the Company or its affiliates or
          engaging in solicitation in violation of this letter.

     Governing Law/Miscellaneous: This letter is subject to the laws of the
     State of New York. This letter, along with the Confidentiality Agreement,
     sets forth the terms of your employment with the Company and supersedes all
     prior agreements, arrangements and communications, whether oral or written,
     between the Company and you. This letter may not be altered, modified, or
     amended except by a written instrument signed by an individual authorized
     to sign on behalf of the Company (other than you) and by you. This letter
     may not be assigned in whole or in part, except that the Company may assign
     it to an acquirer of all or substantially all of the assets of the Company.
     This letter shall be binding on the successors and permitted assignees of
     the parties hereto.

     This offer is made to you based on your representation to the Company that
     your acceptance of employment with the Company and performance of the
     contemplated services does not and will not conflict with or result in any
     breach or default under any agreement, contract or arrangement to which you
     are a party or violate any other legal restriction. If you find this offer
     of employment acceptable, please sign the enclosed copy of this letter and
     return it to us.

/s/ J. Curt Hockemeier
J. Curt Hockemeier
President and Chief Executive Officer

<PAGE>

Agreed and Accepted:

/s/ Peter P. Sach
-----------------------------
Peter P. Sach

Dated: July 12, 2001

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