The present invention is directed to a system and method for use in a telecommunication networks to facilitate the use of packet switched end-user devices, particularly push-to-talk (PTT) devices, across multiple communication services and legacy networks. The present invention provides an enhanced proxy for integrated voice over internet protocol (VoIP) applications that enable predefined custom numbers to be utilized on a PTT device to access services on one or more legacy networks. The present invention also provides a means for the delivery of information that is dynamically customized and specific to an end-user of the PTT device.