EXHIBIT 5.1





                        [Letterhead of William F. Sorin]



                                                              October 6, 2000



Ladies and Gentlemen:

                  I have acted as counsel to Comverse Technology, Inc., a New
York corporation (the "Company"), in connection with the registration, pursuant
to a Registration Statement on Form S-8 under the Securities Act of 1933, as
amended (the "Registration Statement"), of an aggregate of 10,505 shares of
Common Stock of the Company, par value $0.10 per share ("Common Stock"),
issuable upon the exercise of options ("Options") which have been granted under
the Stock Option Plan of Gaya Software Industries Ltd. (the "Plan").

                  I have examined originals, or copies certified to my
satisfaction, of the Certificate of Incorporation and By-Laws of the Company,
the minutes and other records of the proceedings of the Board of Directors and
of the Stockholders of the Company, the Plan and such other documents, corporate
and public records, agreements and certificates of officers of the Company and
of public and other officials, and I have considered such questions of law, as I
have deemed necessary as a basis for the opinions hereinafter expressed. In such
examination I have assumed the genuineness of all signatures and the
authenticity of all documents submitted to me as originals and the conformity to
original documents of all documents submitted to me as certified or photostatic
copies.

                  Based on and subject to the foregoing, I hereby advise you
that, in my opinion, the issuance of shares of Common Stock, upon exercise of
the Options in accordance with the provisions and subject to the conditions set
forth in the Plan and in the agreements executed thereunder governing the
issuance and exercise of the Options, has been duly authorized and, when the
consideration for such shares has been received by the Company and such shares
have been issued in accordance with and subject to such terms and conditions,
such shares of Common Stock will be legally issued, fully paid and
nonassessable.

                  I hereby consent to the filing of this opinion with the
Securities and Exchange Commission in connection with the Registration
Statement.

                                          Very truly yours,

                                          /s/ William F. Sorin

                                          William F. Sorin