EXHIBIT 5.1

William F. Sorin
17 East 89th Street
New York, NY  10128

June 28, 2001

Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C.  20549-1004

Re:  Comverse Technology, Inc.
     -------------------------

Gentlemen:

I have acted as legal 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 (the "Registration Statement") under the
Securities Act of 1933, as amended, of an aggregate of 17,250,000 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 or may be
granted under the 1989 Stock Option Plan, 1992 Directors' Stock Option Plan,
1994 Stock Incentive Plan, 1995 Director Stock Option Plan, Amended and Restated
1996 Stock Incentive Plan and the Nonstatutory Stock Option Agreement of Boston
Technology, Inc. and the 1987 Stock Option Plan, 1994 Stock Option Plan, 1995
Stock Option Plan, 1996 Stock Option Plan, 1997 Stock Incentive Compensation
Plan, 1997 Employee Stock Purchase Plan, 1999 Stock Incentive Compensation Plan,
2000 Stock Incentive Compensation Plan and 2001 Stock Incentive Compensation
Plan of the Company (collectively, the "Plans").

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 Plans 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
Plans 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