SAN JOSE, Calif. (AP) _ Cisco Systems Inc. announced today it is acquiring privately held Calista Inc., a provider of Internet-based phone technology, for $55 million in stock.

Calista, based in Bucks, England and San Jose, develops technology that allows phone systems from different vendors to work together over an open, Internet-based infrastructure.

The acquisition enables Cisco to offer its customers the ability to transmit data, voice and video services through the Internet rather than traditional phone lines, the company said in a statement.

Cisco, based in San Jose, is a leading maker of data networking equipment. The transaction is expected to close in the first quarter of Cisco's fiscal year 2000.