<Page>

                                                                     EXHIBIT 4.4

     THIS SECURITY IS A GLOBAL SECURITY WITHIN THE MEANING OF THE WARRANT AND
REGISTRATION RIGHTS AGREEMENT HEREINAFTER REFERRED TO AND IS REGISTERED IN THE
NAME OF A DEPOSITORY OR A NOMINEE OF A DEPOSITORY OR A SUCCESSOR DEPOSITORY.
THIS SECURITY IS NOT EXCHANGABLE FOR SECURITIES REGISTERED IN THE NAME OF A
PERSON OTHER THAN THE DEPOSITORY OR ITS NOMINEE EXCEPT IN THE LIMITED
CIRCUMSTANCES DESCRIBED IN THE WARRANT AND REGISTRATION RIGHTS AGREEMENT, AND NO
TRANSFER OF THIS SECURITY (OTHER THAN A TRANSFER OF THIS SECURITY AS A WHOLE BY
THE DEPOSITORY TO A NOMINEE OF THE DEPOSITORY OR BY A NOMINEE OF THE DEPOSITORY
TO THE DEPOSITORY OR ANOTHER NOMINEE OF THE DEPOSITORY) MAY BE REGISTERED EXCEPT
IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE WARRANT AND REGISTRATION RIGHTS
AGREEMENT. UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE
OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO THE ISSUER
OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE, OR PAYMENT, AND ANY
CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME
AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE
TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR
OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER
HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

     THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE UNITED STATES SECURITIES
ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), AND, ACCORDINGLY, MAY NOT BE
OFFERED OR SOLD EXCEPT AS SET FORTH BELOW. BY ITS ACQUISITION HEREOF, THE HOLDER
(1) REPRESENTS THAT IT IS A "QUALIFIED INSTITUTIONAL BUYER" (AS DEFINED IN RULE
144A UNDER THE SECURITIES ACT), (2) AGREES THAT IT WILL NOT WITHIN TWO YEARS
AFTER THE ORIGINAL ISSUANCE OF THIS SECURITY RESELL OR OTHERWISE TRANSFER THIS
SECURITY EXCEPT (A) TO THE ISSUER OR ANY SUBSIDIARY THEREOF, (B) TO A QUALIFED
INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, OR
(C) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BEEN DECLARED EFFECTIVE UNDER
THE SECURITIES ACT (AND WHICH CONTINUES TO BE EFFECTIVE AT THE TIME OF SUCH
TRANSFER) AND (3) AGREES THAT IT WILL DELIVER TO EACH PERSON TO WHOM THIS
SECURITY IS TRANSFERRED A NOTICE SUBSTANTIALLY TO THE EFFECT OF THIS LEGEND.

     THE SHARES OF STOCK PURCHASABLE UPON EXERCISE OF THE WARRANTS REPRESENTED
BY THIS CERTIFICATE ARE ALSO SUBJECT TO THE WARRANT AND REGISTRATION RIGHTS
AGREEMENT AND THE SECURITIES EXCHANGE AGREEMENT TO WHICH THE ISSUER AND THE
WARRANT AGENT ARE PARTY, A COPY OF WHICH MAY BE INSPECTED AT THE PRINCIPAL
OFFICE OF THE ISSUER OR OBTAINED FROM THE ISSUER WITHOUT CHARGE.

<Page>

                                  iBASIS, INC.

No. W-1                                                       3,071,184 Warrants

CUSIP NO: 450732 11 0

                               WARRANT CERTIFICATE

     This Warrant Certificate certifies that CEDE & Co., or its registered
assigns, is the registered holder of warrants expiring January 15, 2008 (the
"Warrants") to purchase shares of Common Stock, par value $0.001 per share (the
"Common Stock"), of iBasis, Inc., a Delaware Corporation (the "Company"). Each
Warrant entitles the holder upon exercise to receive from the Company on or
after the date of issuance of such Warrant and on or before 5:00 P.M. Boston
Time on January 15, 2008 (the "Expiration Date"), one fully paid and
nonassessable share of Common Stock (a "Warrant Share") at the initial exercise
price (the "Exercise Price") of $0.65 payable in lawful money of the United
States of America upon surrender of this Warrant Certificate and payment of the
Exercise Price at the office or agency of the Warrant Agent, but only subject to
the conditions set forth herein and in the Warrant and Registration Rights
Agreement referred to on the reverse hereof. The Exercise Price and number of
Warrant Shares issuable upon exercise of the Warrants are subject to adjustment
upon the occurrence of certain events set forth in the Warrant and Registration
Rights Agreement.

     No Warrant may be exercised after the Expiration Date, and to the extent
not exercised by such time such warrants shall become void.

     This Warrant Certificate shall not be valid unless countersigned by the
Warrant Agent, as such term is used in the Warrant and Registration Rights
Agreement.

     This Warrant Certificate, and all actions, claims and conduct relating
thereto, shall be governed by and construed in accordance with the laws of The
Commonwealth of Massachusetts, without regard to the principles of conflicts of
laws.

                                       -2-
<Page>

     IN WITNESS WHEREOF, iBasis, Inc., has caused this Warrant Certificate to be
duly executed.

Dated:  January 30, 2003

                                           iBASIS, INC.


                                           By: /s/ Ofer Gneezy
                                              ------------------------------
                                              Name:  Ofer Gneezy
                                              Title: President and CEO


WARRANT AGENT'S CERTIFICATE OF AUTHENTICATION
This is one of the Warrants described in the within-named Warrant Agreement.

U.S. BANK NATIONAL ASSOCIATION, as Warrant Agent


By: /s/ John A. Brennan
    -------------------------------------
    Name:  John A. Brennan
    Title: Trust Officer


By:
    -------------------------------------
          As Authenticating Agent
     (if different from Warrant Agent)

                                       -3-
<Page>

                                  iBASIS, INC.

     The Warrants evidenced by this Warrant Certificate are part of a duly
authorized issue of Warrants expiring January 15, 2008, entitling the holder on
exercise to receive shares of Common Stock and are issued or to be issued
pursuant to a Warrant and Registration Rights Agreement dated as of January 29,
2003 (the "Warrant and Registration Rights Agreement"), duly executed and
delivered by the Company to U.S. Bank National Association, as warrant agent
(the "Warrant Agent"), which Warrant and Registration Rights Agreement is hereby
incorporated by reference in and made a part of this instrument and is hereby
referred to for a description of the rights, limitation of rights, obligations,
duties and immunities thereunder of the Warrant Agent, the Company and the
holders (the words "holders" or "holder" meaning the registered holders or
registered holder) of the Warrants. A copy of this Warrant and Registration
Rights Agreement may be obtained by the holder hereof upon written request to
the Company. Capitalized terms used herein without being otherwise defined shall
have the meaning ascribed to them in the Warrant and Registration Rights
Agreement.

     Each Warrant may be exercised at any time on or after the date of issuance
of such Warrant and on or before the Expiration Date. The holder of Warrants
evidenced by this Warrant Certificate may exercise them as follows:

          (I) The Warrants evidenced by this Warrant Certificate may be
     exercised by the holder hereof, in whole or in part, during normal business
     hours on any Business Day on or prior to the Expiration Date, by surrender
     of this Warrant Certificate to the Company at its principal office,
     accompanied by a subscription substantially in the form attached to this
     Warrant Certificate duly executed by such holder and accompanied by (a)
     wire transfer of immediately available funds or (b) certified or official
     bank check payable to the order of the Company, in each case in the amount
     obtained by multiplying (i) the number of shares of Common Stock (without
     giving effect to any adjustment thereof pursuant to the provisions of the
     Warrant and Registration Rights Agreement) for which the Warrant evidenced
     by this Warrant Certificate is then being exercised, as designated in such
     subscription, by (ii) the Initial Exercise Price. Thereupon, such holder
     shall be entitled to receive the number of duly authorized, validly issued,
     fully paid and nonassessable shares of Common Stock (or Other Securities)
     determined as provided in Sections 6 and 7 of the Warrant and Registration
     Rights Agreement.

          (II) The Warrants evidenced by this Warrant Certificate may be
     converted by the holder hereof, in whole or in part, into shares of Common
     Stock (or Other Securities), during normal business hours on any Business
     Day on or prior to the Expiration Date, by surrender of this Warrant
     Certificate to the Company at its principal office, accompanied by a
     conversion notice substantially in the form attached to this Warrant
     Certificate duly executed by such holder. Thereupon, such holder shall be
     entitled to receive a number of duly authorized, validly issued, fully paid
     and nonassessable shares of Common Stock (or Other Securities) equal to:

     (a) the excess of

                                       -4-
<Page>

               (i) (x) the number of shares of Common Stock (or Other
          Securities) determined as provided in Sections 6 and 7 of the Warrant
          and Registration Rights Agreement which such holder would be entitled
          to receive upon exercise of the Warrants represented by this Warrant
          Certificate for the number of shares of Common Stock designated in
          such conversion notice (without giving effect to any adjustment
          thereof pursuant to Sections 6 or 7 of the Warrant and Registration
          Rights Agreement) MULTIPLIED BY (y) the Current Market Price of each
          such share of Common Stock (or such Other Securities) so receivable
          upon such exercise

          OVER

               (ii) (x) the number of shares of Common Stock (without giving
          effect to any adjustment thereof pursuant to Sections 6 or 7 of the
          Warrant and Registration Rights Agreement or other provisions thereof)
          which such holder would be entitled to receive upon exercise of the
          Warrants represented by this Warrant Certificate for the number of
          shares of Common Stock designated in such conversion notice (without
          giving effect to any adjustment thereof pursuant to Sections 6 or 7 of
          the Warrant and Registration Rights Agreement) MULTIPLIED BY (y) the
          Initial Exercise Price

          DIVIDED BY

          (b) such Current Market Price of each such share of Common Stock (or
     Other Securities).

          (III) The Warrant represented by this Warrant Certificate may be
     exercised by the holder hereof, in whole or in part, during normal business
     hours on any Business Day on or prior to the Expiration Date, by surrender
     of this Warrant Certificate to the Company at its principal office,
     accompanied by a note tender notice substantially in the form attached to
     this Warrant Certificate duly executed by such holder and accompanied by a
     Note. Thereupon, such holder shall be deemed to have exercised the Warrant
     represented by this Warrant Certificate for the number of shares of Common
     Stock (up to the maximum number of shares of Common Stock set forth on the
     face of this Warrant Certificate and without giving effect to any
     adjustment thereof pursuant to Sections 6 or 7 of the Warrant and
     Registration Rights Agreement or other provisions thereof) obtained by
     dividing (i) the sum of the outstanding face amount of such Note (or such
     lesser amount indicated on the note tender notice) PLUS any cash or
     payment-in-kind interest accrued on such Note, PLUS any accrued prepayment
     penalty or premium by (ii) the Exercise Price. Thereupon, such holder shall
     be entitled to receive the number of duly authorized, validly issued, fully
     paid and nonassessable shares of Common Stock (or Other Securities)
     determined as provided in Sections 6 and 7 of the Warrant and Registration
     Rights Agreement.

     In the event that upon any exercise of Warrants evidenced hereby the number
of Warrants exercised shall be less than the total number of Warrants evidenced
hereby, there shall be issued to the holder hereof or its assignee a new Warrant
Certificate of like tenor, dated the date hereof and calling in the aggregate on
the face or faces thereof for the number of Warrants (without giving effect to

                                       -5-
<Page>

any adjustment thereof pursuant to the terms of the Warrant and Registration
Rights Agreement) to the number of Warrants called for on the face of this
Warrant Certificate minus the number of Warrants designated by the holder upon
such exercise.

     Upon the exercise of the Warrants evidenced by this Warrant Certificate as
provided above, the Company may elect either (i) to comply with the requirements
of Section 7.3(a) of the Warrant and Registration Rights Agreement with respect
to the issuance of shares of Common Stock in connection with such exercise or
(ii) upon written notice to the holder not more than two Business Days following
the date of exercise, to pay to the holder an amount equal to the Market Price
for each share of Common Stock issuable upon such exercise (the "Cash Close
Out") in lieu of issuing such Common Stock. Any Cash Close Out made in
accordance with this paragraph shall be paid within two Business Days of the
exercise of the Warrants evidenced by this Warrant Certificate by (a) wire
transfer of immediately available funds or (b) certified or official bank check
payable to the order of the holder hereof.

     The Company will not be required to issue fractional shares of Common Stock
upon exercise of the Warrants or distribute share certificates that evidence
fractional shares of Common Stock. In lieu of fractional shares of Common Stock,
there may be paid to the registered Holder of this Warrant Certificate at the
time such Warrant Certificate is exercised an amount in cash equal to the same
fraction of the Current Market Value per share of Common Stock on the Business
Day immediately proceeding the date this Warrant Certificate is surrendered for
exercise.

     The holders of the Warrants are entitled to certain registration rights
with respect to the Common Stock purchasable upon exercise thereof. Such
registration rights are set forth in Section 8 of the Warrant and Registration
Rights Agreement.

     Warrant Certificates, when surrendered at the office of the Warrant Agent
by the registered holder thereof in person or by legal representative or
attorney duly authorized in writing, may be exchanged, in the manner and subject
to the limitations provided in the Warrant and Registration Rights Agreement,
but without payment of any service charge, for another Warrant Certificate or
Warrant Certificates of like tenor evidencing in the aggregate a like number of
Warrants.

     Upon due presentation for registration of transfer of this Warrant
Certificate at the office of the Warrant Agent a new Warrant Certificate or
Warrant Certificates of like tenor and evidencing in the aggregate a like number
of Warrants shall be issued to the transferee(s) in exchange for this Warrant
Certificate, subject to the limitations provided in the Warrant and Registration
Rights Agreement, without charge except for any tax or other governmental charge
imposed in connection therewith.

     The Company and the Warrant Agent may deem and treat the registered
holder(s) thereof as the absolute owner(s) of this Warrant Certificate
(notwithstanding any notation of ownership or other writing hereon made by
anyone), for the purpose of any exercise hereof, of any distribution to the
holder(s) hereof, and for all other purposes, and neither the Company nor the
Warrant Agent shall be affected by any notice to the contrary. Neither the
Warrants nor this Warrant Certificate entitled any holder hereof to any rights
of a stockholder of the Company.

                                       -6-
<Page>

                              FORM OF SUBSCRIPTION

                 [To be executed only upon exercise of Warrant]

To iBasis, Inc.:

         The undersigned hereby irrevocably elects to exercise the right,
represented by this Warrant Certificate, to receive __________(1) shares of the
Common Stock and herewith makes payment of $_____ in accordance with the terms
hereof, and requests that the certificates for such shares be issued in the name
of, and delivered to _______________, whose address is as follows:

Dated:
                         --------------------------------------------------
                         (Signature must conform in all respects to name of
                         holder as specified on the face of Warrant)


                         --------------------------------------------------
                         (Street Address)


                         --------------------------------------------------
                         (City)            (State)          (Zip Code)


----------
(1) Insert here the number of shares called for on the face of this Warrant
Certificate (or, in the case of a partial exercise, the portion thereof as to
which the Warrant evidenced by this Warrant Certificate is being exercised), in
either case without making any adjustment for any stock or other securities or
property or cash which, pursuant to the adjustment provisions of the Warrant
evidenced by this Warrant Certificate, may be delivered upon exercise. In the
case of a partial exercise, a new Warrant Certificate will be issued and
delivered, representing the unexercised portion of the Warrant evidenced by this
Warrant Certificate, to the holder surrendering the Warrant Certificate.

                                       -7-
<Page>

                               FORM OF ASSIGNMENT

                 [To be executed only upon transfer of Warrant]

     For value received, the undersigned registered holder of the Warrants
evidenced by this Warrant Certificate hereby sells, assigns and transfers unto
__________________the right represented by such Warrant Certificate to purchase
_______(2) shares of Common Stock of iBasis, Inc. to which such Warrant
Certificate relates, and appoints _______________Attorney to make such transfer
on the books of iBasis, Inc. maintained for such purpose, with full power of
substitution in the premises.

Dated:
                         --------------------------------------------------
                         (Signature must conform in all respects to name of
                         holder as specified on the face of Warrant)


                         --------------------------------------------------
                         (Street Address)


                         --------------------------------------------------
                         (City)            (State)          (Zip Code)


Signed in the presence of:

----------
(2) Insert here the number of shares called for on the face of this Warrant
Certificate (or, in the case of a partial transfer, the portion thereof as to
which the Warrant evidenced by this Warrant Certificate is being transferred),
in either case without making any adjustment for any stock or other securities
or property or cash which, pursuant to the adjustment provisions of the Warrant
evidenced by this Warrant Certificate, may be delivered upon exercise. In the
case of a partial transfer, a new Warrant Certificate will be issued and
delivered, representing the non-transferred portion of the Warrants evidenced by
this Warrant Certificate, to the holder transferring the Warrants.

                                       -8-
<Page>

                            FORM OF CONVERSION NOTICE

To iBasis, Inc.:

     The undersigned registered holder of the Warrants evidenced by this Warrant
Certificate hereby irrevocably converts such Warrants with respect to
________(3) shares of the Common Stock which such holder would be entitled to
receive upon the exercise hereof, and requests that the certificates for such
shares be issued in the name of, and delivered to _________________, whose
address is as follows:

Dated:
                          --------------------------------------------------
                          (Signature must conform in all respects to name of
                          holder as specified on the face of Warrant)


                          --------------------------------------------------
                          (Street Address)


                          --------------------------------------------------
                          (City)            (State)          (Zip Code)


----------
(3) Insert here the number of shares called for on the face of this Warrant
Certificate (or, in the case of a partial conversion, the portion thereof as to
which the Warrants evidenced by this Warrant Certificate are being converted),
in either case without making any adjustment for additional shares of Common
Stock or any other stock or other securities or property or cash which, pursuant
to the adjustment provisions of the Warrant evidenced by this Warrant
Certificate, may be delivered upon exercise. In the case of a partial
conversion, a new Warrant Certificate will be issued and delivered, representing
the unconverted portion of the Warrants, to the holder surrendering this Warrant
Certificate.

                                       -9-
<Page>

                               FORM OF NOTE TENDER

          [To be executed only upon a note tender exercise of Warrant]

To iBasis, Inc.:

     The undersigned registered holder of the Warrants evidenced by this Warrant
Certificate hereby irrevocably exercises such Warrants for, and purchases
thereunder, __________(4) shares of the Common Stock and herewith makes payment
of $_____ therefore by virtue of tendering the attached Note, and requests that
the certificates for such shares be issued in the name of, and delivered to
_______________, whose address is as follows:

Dated:
                         --------------------------------------------------
                         (Signature must conform in all respects to name of
                         holder as specified on the face of Warrant)



                         (Street Address)



                         (City)            (State)          (Zip Code)

----------
(4) Insert here the number of shares called for on the face of this Warrant
Certificate (or, in the case of a partial exercise, the portion thereof as to
which the Warrants evidenced by this Warrant Certificate are being exercised),
in either case without making any adjustment for any stock or other securities
or property or cash which, pursuant to the adjustment provisions of the Warrants
evidenced by this Warrant Certificate, may be delivered upon exercise. In the
case of a partial exercise, a new Warrant Certificate will be issued and
delivered, representing the unexercised portion of the Warrants, to the holder
surrendering this Warrant Certificate.

                                      -10-
<Page>


                              SCHEDULE OF EXCHANGES

The following exchanges of a part of this Global Warrant for Physical Warrants
(or of Physical Warrants for an interest in the Global Warrant) have been made:

<Table>
<S>                       <C>                    <C>                      <C>                    <C>
                                                                          Number of Warrants
                           Amount of decrease                               of this Global
                              in Number of       Amount of increase in     Warrant following        Signature of
                          Warrants this Global   Number of Warrants of     such decrease (or     authorized officer
    Date of Exchange             Warrant          this Global Warrant          increase)          of Warrant Agent
-------------------------------------------------------------------------------------------------------------------
</Table>

                                      -11-