SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                    FORM 8-K

                                 CURRENT REPORT
                     PURSUANT TO SECTION 13 OR 15(d) OF THE
                         SECURITIES EXCHANGE ACT OF 1934

                                December 18, 2006
                              ---------------------
                Date of Report (Date of earliest event reported)
                              ---------------------

                                  iBASIS, INC.
                              ---------------------
               (Exact Name of Registrant as Specified in Charter)


          DELAWARE                     0-27127                   04-3332534

- --------------------------------------------------------------------------------
(State or Other Jurisdiction         (Commission                (IRS Employer
       of Incorporation)             File Number)            Identification No.)


                     20 Second Avenue, Burlington, MA 01803
              -----------------------------------------------------
               (Address of Principal Executive Offices) (Zip Code)

                                 (781) 505-7500
              (Registrant's telephone number, including area code)

     Check the appropriate box below if the Form 8-K filing is intended to
simultaneously satisfy the filing obligation of the registrant under any of the
following provisions (see General Instruction A.2. below):

[ ] Written communications pursuant to Rule 425 under the Securities Act (17
    CFR 230.425)
[x] Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR
    240.14a-12)
[ ] Pre-commencement communications pursuant to Rule 14d-2(b) under the
    Exchange Act (17 CFR 240.14d-2(b))
[ ] Pre-commencement communications pursuant to Rule 13e-4(c) under the
    Exchange Act (17 CFR 240.13e-4(c))




Item 1.01 Entry Into Material Definitive Agreement

     On December 18,  2006,  iBasis,  Inc.  ("iBasis")  and KPN Telecom  B.V., a
private limited  liability  company  organized under the laws of the Netherlands
("KPN"), entered into an amendment ("Amendment No. 1") to the Share Purchase and
Sale Agreement between the parties dated as of June 21, 2006 (the  "Agreement").
As previously reported,  pursuant to the Agreement, KPN will acquire that number
of newly issued shares of iBasis  common stock,  $0.001 par value per share (the
"Common Stock"),  that shall represent,  immediately after issuance,  51% of the
issued and outstanding  shares of the Common Stock on a  fully-diluted  basis on
the date of closing (the  "Closing")  of the  transactions  contemplated  by the
Agreement (the "Transaction").  Amendment No. 1 extends the outside date for the
Closing of the Transaction from December 31, 2006 to April 30, 2007. Pursuant to
Amendment No. 1, iBasis has also agreed to provide KPN with regular  updates and
information  on its  stock  option  grant  review,  including  accounting,  tax,
regulatory and legal  proceedings and developments.  In all other respects,  the
Agreement remains unchanged and the parties have not waived any rights under the
Agreement.

     The  foregoing  description  of  Amendment  No. 1 and the  Agreement is not
complete and is qualified in its entirety by reference to such agreements.

     In connection with Amendment No. 1, iBasis has issued a press release which
is filed as Exhibit 99.1 hereto and is incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits.

     (d)  Exhibits.

          Exhibit
          -------
          Number         Description
          ------         -----------

          10.1           Amendment No. 1 dated as of December 18, 2006, to the
                         Share Purchase and Sale Agreement dated as of June 21,
                         2006, between iBasis, Inc. and KPN Telecom B.V.

          99.1           Press release dated December 18, 2006

Additional Information and Where to Find It

     This communication may be deemed to be solicitation  material in respect of
the proposed Transaction.  In connection with the proposed  Transaction,  iBasis
intends to file or furnish  relevant  materials with the SEC,  including a proxy
statement on Schedule 14A. STOCKHOLDERS OF iBASIS ARE URGED TO READ ALL RELEVANT
DOCUMENTS  FILED WITH THE SEC WHEN THEY  BECOME  AVAILABLE,  INCLUDING  iBASIS'S
PROXY STATEMENT,  BECAUSE THEY WILL CONTAIN IMPORTANT  INFORMATION ABOUT iBASIS,
THE PROPOSED  TRANSACTION AND RELATED  MATTERS.  Investors and security  holders
will be able to  obtain  the  documents  free of  charge  at the SEC's web site,
http://www.sec.gov,  and iBasis's  stockholders  will receive  information at an
appropriate  time on how to obtain  Transaction-related  documents for free from
iBasis  and  will be able  to view  such  documents  on the  iBasis  website  at
www.ibasis.com. Such documents are not currently available.

Participants in Solicitation

     KPN and its directors and executive officers,  and iBasis and its directors
and executive officers,  may be deemed to be participants in the solicitation of
proxies  from the holders of iBasis's  Common  Stock in respect of the  proposed
Transaction.  Information  about the directors  and executive  officers of KPN's
parent  entity,  Koninklijke  KPN N.V. is set forth in its Form 20-F,  which was
filed  with the SEC on March  14,  2006.  Information  about the  directors  and
executive  officers of iBasis is set forth in iBasis's  proxy  statement for its
2006 Annual Meeting of  Stockholders,  which was filed with the SEC on March 23,
2006. Investors may obtain additional information regarding the interest of such
participants  by reading the proxy statement  regarding the Transaction  when it
becomes available.




Safe Harbor for Forward-Looking Statements

     Statements  in this  Current  Report  on Form 8-K  regarding  the  proposed
Transaction  between  iBasis and KPN,  including  the  statements  regarding the
Transaction and products and any other statements  regarding the parties' future
expectations,  beliefs, goals or prospects constitute forward-looking statements
under Section 21E of the  Securities  Exchange Act of 1934 and involve risks and
uncertainties.  Any  statements  that  are not  statements  of  historical  fact
(including statements  containing the words "believes," "plans,"  "anticipates,"
"expects,"  "estimates"  and  similar  expressions)  should  also be  considered
forward-looking  statements.  A number of important  factors  could cause actual
results  or  events  to  differ   materially   from  those   indicated  by  such
forward-looking  statements,  including the parties'  ability to consummate  the
Transaction due to regulatory  restrictions,  the failure to receive stockholder
approval,  issues related to the Company's stock option review or other reasons,
the ability of iBasis and KPN to  successfully  integrate  their  operations and
employees,  the ability to realize anticipated  synergies,  the emergence of new
competitive  initiatives resulting from rapid technological  advances or changes
in pricing in the market,  business conditions and volatility and uncertainty in
the  markets  that  iBasis and KPN serve,  and the other  factors  described  in
iBasis's  Quarterly  Report on Form 10-Q for its most recently  completed fiscal
quarter and Annual  Report on Form 10-K for its most recently  completed  fiscal
year, and the Form 20-F filing of  Koninklijke  KPN N.V. filed with the SEC, all
of which are available at www.sec.gov.  Such forward-looking statements are only
as of the date they are made,  and iBasis  expressly  disclaims any intention or
obligation to update any forward-looking  statements as a result of developments
occurring after the date of this release.




                                    SIGNATURE
                                    ---------

     Pursuant to the  requirements  of the Securities  Exchange Act of 1934, the
registrant  has duly  caused  this  report  to be  signed  on its  behalf by the
undersigned hereunto duly authorized.

Date: December 18, 2006                  iBASIS, INC.


                                         By: /s/ Richard Tennant
                                             -----------------------------------
                                             Senior Vice President, Finance and
                                             Administration
                                             And Chief Financial Officer
                                             (Principal Financial and Accounting
                                             Officer)