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Exhibit 10.5

                                                                  14 August 2001

                             TO WHOM IT MAY CONCERN

I hereby retire, and resign with immediate effect from any and all corporate
functions (including as a management or board member, or officer or any other
similar function) which I currently hold with Carrier1 International GmbH or
with any of the entities listed on Appendix A [Company will supply Appendix A]
or any other entity directly or indirectly holding a majority or minority equity
interest in ("own") or controlling, or owned or controlled by, or under common
ownership or control with Carrier1 International GmbH (each a "Carrier1 entity")
or any other legal entity to which I have been nominated or appointed for any
such corporate function by a Carrier1 entity.

I hereby irrevocably appoint each of Kees van Ophem, Alex Schmid and each member
of the board of Carrier1 International S.A., individually, as my attorney to
execute all such documents and to do all such other acts and deeds as may be
required to give full effect to the foregoing paragraph.

/s/  Stig Johansson
---------------------------------
Stig Johansson<Page>

                              SEPARATION AGREEMENT

                                     between

                           CARRIER1 INTERNATIONAL GMBH

                    HEREINAFTER REFERRED TO AS THE ,,COMPANY"

                                       and

                               MR. KEES VAN OPHEM

                     HEREINAFTER REFERRED TO AS ,,EMPLOYEE"

          The following Separation Agreement is agreed upon:

    1)    The employment relationship between the Company and the Employee is
          terminated by mutual agreement on 1 October, 2001 and the employment
          agreement dated March 4,1998 between the Employee and the Company
          (known at that time as Carrier1 AG) (the "employment agreement") is
          terminated as of such date except Sections 4.02 [Noncompetition and
          Nonsolicitation Covenants], 4.03 [Infringement of Executive's
          Obligation], 4.04 [Specific Performance], 5.04 [Governing Law; Consent
          to Jurisdiction].

    2)    The Employee will be released from the workplace with immediate effect
          and the Company waives its right to any notice for termination by the
          Employee. The Employee agrees (i) to make himself available during the
          same twelve month period for transition activities and in any other
          way that the Company reasonably requests and (ii) to resign with
          immediate effect (or at such other later date as may be reasonably
          requested by the Company) from any and all corporate functions
          (including as a management or board member, or officer or any other
          similar function) which the Employee has with the Company or any other
          entity directly or indirectly holding a majority or minority equity
          interest in (including with correlative meanings, "owning") or
          controlling, or owned or controlled by, or under common ownership or
          control with the Company (each a "Carrier1 entity", and together
          "Carrier1") or any other legal entity to which he has been nominated
          or appointed by a Carrier1 entity for any such corporate function. The
          Employee hereby agrees to execute such documents or take such steps as
          may be necessary and appropriate to effectuate preceding clause (ii).
          Any vacation days not yet taken will be paid out. The applicable
          proceeds from the Employee's pension plan will be transferred in
          accordance with the applicable laws and statutes pursuant to the
          Employee's instructions.

    3)    The Employee will be entitled hereunder: (i) to retain custody of the
          34,130 shares in Carrier1 International SA that he purchased pursuant
          to the Securities Purchase Agreement (referred to hereafter), (ii) to
          213,333 vested options (with an exercise price of $2 US Dollar per
          ordinary share) that were granted to the Employee in March 1998 under
          the Carrier1 International SA 1999 Option Plan (together with all
          ancillary documents, the "1999 Option Plan") and (iii) until 1 October
          2003, to exercise the options referred to in (ii); provided that, in
          each case of clauses (i)-(iii) above, these shares, options and shares
          issuable upon exercise of the options

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          remain subject to the restrictions of the applicable agreements
          (including the Securityholders Agreement dated as of March 1st, 1999
          among Carrier1 International SA, Carrier One LLC and the other
          securityholders, including the employee, the Securities Purchase
          Agreement dated as of March 1st, 1999 among Carrier1 International SA,
          Carrier One LLC and the purchasers from time to time, including the
          Employee, and the 1999 Option Plan, each as amended, novated,
          supplemented and restated from time to time). All unvested options
          which were granted to the Employee in March 1998, December 2000 and in
          April 2001, respectively, are hereby cancelled for no additional
          consideration. All applicable personal taxes are to be borne by the
          Employee and the Employee indemnifies and holds each Carrier1 entity
          harmless from and against any and all taxes payable by any Carrier1
          entity which are in any way attributable or arise from the holding,
          exercising or disposing of any of the options or shares referred to
          above.

    4)    The Company hereby irrevocably and unconditionally cancels (i) the
          outstanding loan of CHF156,522.05 made by the Company to the Employee
          on or about 25 October 2000 together with any and all interest accrued
          thereon through the date hereof and waives any and all rights as
          against the Employee in respect thereof (including in respect of
          payment, and (ii) any and all shares and options referred to in
          paragraph 3 above and the proceeds from sales of such securities) and
          waives any and all rights as against the Employee and to such assets.
          All applicable personal taxes are to be borne by the Employee and the
          Employee indemnifies and holds each Carrier 1 entity harmless from and
          against any and all taxes payable by any Carrier1 entity which are in
          any way attributable or arise from the cancellation of such loan and
          which are the primary responsibility of the Employee.

    5)    Except as provided in this agreement and except any compulsory
          provisions of the employment law, the Employee , for himself and his
          heirs and personal representatives, hereby fully and forever release
          the Company and their respective subsidiaries, affiliates, officers,
          directors, employees, agents and representatives, from any and all
          claims, liabilities, promises, contracts, and suits which have been or
          could have been asserted by Employee or on his behalf, in any forum by
          reason of matters arising prior to the date of this Agreement. The
          Company on its behalf and on behalf of each Carrier1 entity hereby
          fully and forever release the Employee from any and all claims,
          liabilities, promises, contracts, and suits which have been or could
          have been asserted by any or all of them or on their behalf, in any
          forum by reason of matters arising prior to the date of this
          Agreement, other than any claim, liability, promise, contract or suit
          based in material part on a state of facts or matter of which the
          Company or any other Carrier1 entity do not currently have actual
          knowledge and for which Employee could have been dismissed for "Cause"
          under the Employment Agreement.

    6)    The Employee shall not make any false, disparaging or derogatory
          remarks in public or private about the Institutional Investors as
          defined in Section 10 of the Securityholder's Agreement, the Company
          or any other Carrier1 entity (including their officers, directors,
          employees, agents, or representatives) or family members, as
          applicable) or about business affairs, prospects, products or services
          of Carrier1, except to the extent required by law, and then only after
          consultation with the Company to the maximum extent possible in order
          to maintain goodwill for each of the parties. Subject to the preceding
          sentence, the Employee may discuss his work experience with Carrier1
          with prospective employers or business partners but he shall refer any
          written or oral requests for other information or commentary regarding
          Carrier1 to Carrier1. The Employee may not divulge to any person not
          employed by Carrier1 to use for his own benefit or for the benefit of
          any person not employed by Carrier1 any confidential or non-public
          information obtained while associated with Carrier1. Confidential
          information shall include, without limitation, any information with
          respect to which Carrier1 has an obligation of confidentiality, any
          operational, technical, marketing, compensation, structural,
          organizational, financial or other information of any kind whatsoever
          concerning Carrier1. Confidential information shall not include
          information which is or becomes generally available

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          to the public other than as a result of a disclosure by the Employee.
          For a period of two years after the date of this letter, the Employee
          shall not directly or indirectly recruit, hire, solicit or induce or
          attempt to recruit, hire, solicit or induce, any Employee of Carrier1
          or any of its affiliated companies to terminate their employment with,
          or otherwise cease their relationship with such company or employ any
          such person in any manner or capacity. In case of each breach of an
          obligation set forth in this section 5) the Employee shall pay to the
          Company CHF50,000.00 and in addition he shall compensate the Company
          for any direct or indirect damages caused to any Carrier1 entity (in
          the context of the breach of an obligation set forth in this section
          5).

    7)    The Employee has to give back the property of any Carrier1 entity
          (e.g. mobile phone, company credit card, code card, office keys) no
          later than ten days from the date hereof and declares that he has not
          given any such items to any third party and that he does not have the
          intention to do so. The Employee shall be permitted to retain the
          company car currently provided to the Employee for the remainder of
          the current lease term thereof, provided that the Employee shall pay
          and be responsible for, and shall indemnify and hold the Company
          harmless from and against, any lease payments or other costs
          associated therewith accrued after 1 October 2001. Upon the expiration
          of the lease term, the Employee shall be permitted to purchase such
          car pursuant to any end-of-lease purchase option, provided that the
          Employee shall pay and be responsible for, and shall indemnify and
          hold the Company harmless from and against, any costs associated
          therewith.

    8)    This agreement and the documents referred to herein contain the entire
          obligation of the parties hereto with respect to the subject matter
          hereof and supersede any prior expressions of intent or understandings
          with respect to this matter. This agreement may not be amended,
          modified or supplemented in any respect except by written agreement
          entered into by the parties hereto. If any one or more of the
          provisions contained in this agreement or any document in connection
          herewith shall be invalid, illegal or unenforceable, the validity,
          legality and enforceability of the remaining provisions contained
          herein shall not in any way be affected or impaired. In the event that
          the Employee breaches any provision of this agreement, the Company or
          any other entity shall be entitled to pursue any remedy available.

    9)    This entire agreement and understanding is governed by the laws of
          Switzerland. Any dispute, controversy or claim arising out of or
          relating to this agreement or the employment agreement shall be
          submitted to the courts of Zurich, Switzerland.

    10)   Please address any inquiries or notices hereunder to the General
          Counsel, Carrier1 International GmbH, Militarstrasse 36, CH - 8004
          Zurich, Switzerland.

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Zurich, Switzerland, 19 September, 2001

CARRIER1 INTERNATIONAL GMBH                   CARRIER1 INTERNATIONAL GMBH

/s/ Xavier Dedullen                            /s/ Thomas Zahay
-----------------------------------------     ---------------------------

-----------------------------------------     ---------------------------
Xavier Dedullen                               Thomas Zahay
Deputy General Counsel                        Vice President - Human Resources

Employee:

/s/  Kees van Ophem
------------------------

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