Abstract: For a push-to-talk arrangement in a dispatch call communication system (100), an originator (10) selects a group of called parties (11-14). A push-to-talk server (50) handles a dispatch call in a conventional manner. If all the called parties (11-14) do not respond, the originator is given an option to leave a message for an unavailable party (116). A multimedia message service server (60) is the storage medium for these messages. Any unavailable called subscribers (11-14) are provided an indication of a waiting message (128).

Abstract: A method of determining PTT availability of members of a contact list in a wireless PTT communication system makes efficient use of resources by updating client devices (118, 122, 126) with new PTT contact list status information only when necessary. The availability of client devices (118, 122, 126) associated with contact lists (528, 530, 532) are determined by a PTT controller (112) according to the content of messages from the client devices (118, 122, 126). New information regarding the availability of a client device associated with a contact list (528, 530, 532) is transmitted to relevant client devices (118, 122, 126) only when a change has occurred in the availability of a member. Likewise, a client device (118, 122, 126) notifies the PTT controller 112 of its availability only when a change occurs.