A source SCR (106) coupled to a half-duplex radio communication system (100) includes a transceiver (202), and a processor (203) coupled to the transceiver. The source SCR and the half-duplex radio communication system are programmed to receive at the half-duplex radio communication system a monitor request message from a source SCR of the plurality of SCRs to determine a call availability status for each of a first list of at least one target SCR of a group member list of the source SCR, submit from the select one radio base station a call availability status request to each of the first list of at least one target SCR, submit from the half-duplex radio communication system to the source SCR a response state corresponding to the call availability status request of each of the first list of at least one target SCR, and update the group member list according to the response state for each of the first list of at least one target SCR.