A private branch exchange or other communication system switch processes a call to determine if an identifier associated with the call has a corresponding entry in a stored list of external endpoints registered with the switch. This realizes a data structure that causes the recording and deleting places on the information storage medium to correspond spuriously to places on a single tape, such as a VTR tape. In particular, availability and scalability are improved by linking the message application at runtime with any number of the message transports, without the message application specifying a transport at development time.