A method is presented for routing a call from a PBX to a voice mailbox on a communication platform wherein a call is received from an originating device at the PBX and the PBX is associated with a voice mail box on a communication platform. A redirecting number associated with the PBX is assigned to an ISDN message set-up string. The call is forwarded to the communication platform along with the ISDN set-up string information. After verification against a subscriber database, the forwarded call, including related ISDN information is delivered to the communication platform voice mail box server for storage and further processing. The redirecting number may represent the voice mail box identifier, and for increased security and privacy, the voice mail box may be different from the number for the PBX extension from which the voice and data messages are received.