Exhibit 5.1 RUSKIN, MOSCOU, EVANS & FALTISCHEK, P.C. 170 Old Country Road Mineola, New York 11505 (516) 663-6600 July 1, 1996 Periphonics Corporation 4000 Veterans Memorial Highway Bohemia, NY 11716 Re: Periphonics Corporation Gentlemen: We have acted as counsel to Periphonics Corporation, a Delaware corporation (the "Company"), in connection with its filing of a Registration Statement (the "Registration Statement") on Form S-3 with respect to 39,125 shares of the Company's Common Stock to be sold by Ascom Telecommunications Limited (the "Selling Stockholder"). In connection therewith, we have examined such corporate records, certificates and documents as we deemed necessary for the purpose of this opinion, including, without limitation, the Company's Amended and Restated Certificate of Incorporation and Amended and Restated By-Laws. Based on our examination, we advise you that, in our opinion, the Common Stock to be sold by the Selling Stockholder is duly and validly issued, fully paid and non-assessable. We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to the reference to our firm under the caption "Legal Matters" in the Prospectus constituting a part of the Registration Statement. Very truly yours, /s/ Ruskin, Moscou, Evans & Faltischek, P.C. ------------------------------------------- RUSKIN, MOSCOU, EVANS & FALTISCHEK, P.C.