EXHIBIT 5.1
                                                                     -----------

                               KIRKLAND & ELLIS
               PARTNERSHIPS INCLUDING PROFESSIONAL CORPORATIONS



                              153 East 53rd Street
                            New York, New York 10022

                                 (212) 446-4800                   Facsimile:
                                                                (212) 446-4900


                                 July 26, 2001


Net2Phone, Inc.
520 Broad Street
Newark, New Jersey 07102


Ladies and Gentlemen:

     We are acting as special counsel to Net2Phone, Inc., a Delaware corporation
(the "Company"), in connection with the proposed registration by the Company of
701,874 shares of its Common Stock, par value $.01 per share (the "Common
Stock"), pursuant to a Registration Statement (File No. 333-78713) on Form S-3,
originally filed with the Securities and Exchange Commission (the "Commission")
on March 6, 2001 under the Securities Act of 1933, as amended (the "Act") (such
Registration Statement, as further amended or supplemented, is hereinafter
referred to as the "Registration Statement"). All of the shares of Common Stock
to be registered pursuant to the Registration Statement are being offered by a
selling stockholder (the "Secondary Shares").

     In that connection, we have examined originals, or copies certified or
otherwise identified to our satisfaction, of such documents, corporate records
and other instruments as we have deemed necessary for the purposes of this
opinion, including (i) the corporate and organizational documents of the Company
and (ii) minutes and records of the corporate proceedings of the Company with
respect to the original issuance of the Secondary Shares.


     For purposes of this opinion, we have assumed the authenticity of all
documents submitted to us as originals, the conformity to the originals of all
documents submitted to us as copies and the authenticity of the originals of all
documents submitted to us as copies. We have also assumed the legal capacity of
all natural persons, the genuineness of the signatures of persons signing all
documents in connection with which this opinion is rendered, the authority of
such persons signing on behalf of the parties thereto other than the Company and
the due authorization, execution and delivery of all documents by the parties
thereto other than the Company.  We have not independently established or
verified any facts relevant to the opinions expressed herein, but have relied
upon statements and representations of officers and other representatives of the
Company and others.

     Based upon and subject to the foregoing qualifications, assumptions and
limitations and the further limitations set forth below, we are of the opinion
that the Secondary Shares have been duly authorized, validly issued and fully
paid and are nonassessable.

     Our opinions expressed above are subject to the qualifications that we
express no opinion as to the applicability of, compliance with, or effect of any
laws except the General Corporation Law of the State of Delaware.

     We hereby consent to the filing of this opinion with the Commission as
Exhibit 5.1 to the Registration Statement. We also consent to the reference to
our firm under the heading "Legal Opinion" in the Registration Statement. In
giving this consent, we do not thereby admit that we are in the category of
persons whose consent is required under Section 7 of the Act or the rules and
regulations of the Commission. This opinion and consent may be incorporated by
reference in a subsequent registration statement on Form S-3 filed pursuant to
Rule 462(b) under the Act with respect to the registration of additional
securities for sale in the offerings contemplated by the Registration Statement.

     We do not find it necessary for the purposes of this opinion, and
accordingly we do not purport to cover herein, the application of the securities
or "Blue Sky" laws of the various states to the sale of the Secondary Shares.

     This opinion is limited to the specific issues addressed herein, and no
opinion may be inferred or implied beyond that expressly stated herein. We
assume no obligation to revise or supplement this opinion should the General
Corporation Law of the State of Delaware be changed by legislative action,
judicial decision or otherwise.

     This opinion is furnished to you in connection with the filing of the
Registration Statement, and is not to be used, circulated, quoted or otherwise
relied upon for any other purposes.

                                   Sincerely,

                                   /s/ Kirkland & Ellis

                                   Kirkland & Ellis