WILLIAM F. SORIN
                               17 EAST 89TH STREET
                               NEW YORK, NY 10128


                                                               February 13, 2001


Ladies and Gentlemen:

         The undersigned has acted as legal counsel to Comverse Technology,
Inc., a New York corporation (the "Company"), in connection with the
Registration Statement on Form S-3 (the "Registration Statement") filed by the
Company with the Securities and Exchange Commission on the date hereof and
relating to an aggregate of $600,000,000 aggregate principal amount of the
Company's 1.50% Convertible Senior Debentures due 2005 (the "Debentures"),
initially convertible into 5,157,963 shares (the "Subject Shares") of the
Company's common stock, par value $.10 per share, to be offered for resale by
the Selling Holders identified therein.

         In the capacity of legal counsel to the Company, the undersigned has
examined originals or copies, certified or otherwise identified to the
satisfaction of the undersigned, of such documents, corporate records and other
instruments as the undersigned has deemed necessary for the purpose of rendering
this opinion. In the course of such examinations, the undersigned has assumed
the genuineness of all documents submitted as originals and the conformity to
originals and certified documents of all copies submitted as conformed copies.

         Based upon and subject to the foregoing, the undersigned is of the
opinion that (i) the Debentures are legally issued and constitute valid and
binding obligations of the Company, enforceable against the Company in
accordance with their terms, except as such enforcement is subject to any
applicable bankruptcy, insolvency, reorganization or other law relating to or
affecting creditors' rights generally and general principles of equity and (ii)
the Subject Shares, when such Subject Shares have been duly issued and delivered
by the Company upon conversion of the Debentures in accordance with the
Indenture will be validly issued, fully paid and nonassessable.

         The undersigned hereby consents to the filing of this opinion as
Exhibit 5.1 to the Registration Statement and the reference to the undersigned
under the caption "Legal Matters" in the Prospectus contained therein. In giving
the foregoing consent, the undersigned does not thereby admit that the
undersigned is within the category of persons whose consent is required under
Section 7 of the Securities Act of 1933, as amended, or the rules and regulation
of the Securities and Exchange Commission thereunder.



                                                     Very truly yours,

                                                     /s/  William F. Sorin