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listed on Annex A hereto
REGISTRATION RIGHTS AGREEMENT
Dated as of May 29, 2003
TABLE OF CONTENTS
REGISTRATION RIGHTS AGREEMENT (this " Agreement "), dated as of May 29, 2003, between (i) iBasis, Inc., a Delaware
corporation (the " Company "), (ii) the persons listed on Annex A hereto (the " Initial Holders "), and (iii) each other Person
who becomes a party to this Agreement pursuant to Section 9 hereof (such other Persons together with the Initial Holders, the "
Holders "). Capitalized terms used herein and not otherwise defined shall have the meaning ascribed to such terms in Section 2
WHEREAS, the Company proposes to issue to the Holders (i) the Commonwealth Warrants, which in the aggregate initially
entitle the Holders to purchase, 1,116,605 shares of Common Stock of the Company on May 29, 2003, and (ii) the Commonwealth
Notes, in the aggregate principal amount of $6,100,000, in each case pursuant to a Joinder Agreement (dated as of May 29, 2003,
by and among the Company, iBasis Global, Inc., the Holders and U.S. Bank National Association, as Collateral Agent (the "
Joinder Agreement ")) to that certain Securities Exchange Agreement, dated as of February 21, 2003, among the Company,
iBasis Global, Inc., the guarantors named therein, JMG Triton Offshore Limited Fund CITCO and U.S. Bank National
Association, as Collateral Agent (as amended, supplemented and otherwise modified from time to time, the " Securities
Exchange Agreement ").
WHEREAS, the Company and the Holders desire to enter into this Agreement to provide the Holders registration rights
with respect to the Commonwealth Warrants and the Commonwealth Notes.
WHEREAS, the Commonwealth Warrants and the Commonwealth Notes shall have registration rights as provided herein.