Have a customer that moved in and there was an existing KXTA624 with a doorphone module installed. The original owners took all the Panasonic phones but left the PBX. Current customer would like to use SLT phones and be able to answer the doorphone as well as be able to activate the door strike. The door phone does do a double ring on an SLT phone and you can talk to the visitor, but not activate the relay. Can I program this function through the serial port of the PBX or do you have to have a proprietary phone?