You'll need two "parts" - first is the strike itself - often installed by locksmith. Although many are made to fit steel door casement - so actual install is fairly straight-forward. Next is "control" to close a contact to power (or remove power) from striker. If all is in place, easiest is a push button that runs the relay. If you want door to be released from any phone, add a Valcom or Viking (or others) door control unit to allow the striker to be operated via touch-tone. What you'll need depends on whether you plan to retrofit an existing door phone or if you're starting new. Partner has a both a contact closure and door phone for just this application.
Good luck.
Mike