A communication system that is particularly suited to switch a full duplex session to a half duplex session. The system includes a VoIP server that sets up a full duplex session; and a dispatch call controller server that receives a request to switch the full duplex session to a half duplex session; forwards the request to the target subscriber unit; receives an acceptance of the request; and sets up the half duplex session between the subscriber units. In another embodiment, the VoIP server receives the request to switch to the half duplex session; forwards the request to the target subscriber unit; receives an acceptance of the request; and instructs the dispatch call controller to set up the half duplex session. In yet another embodiment, a service broker receives the request, instructs the dispatch call controller to set up the half duplex session, and instructs the VoIP server to terminate the full duplex session. In yet another embodiment, the switch from full-to-half is network-driven instead of user-driven.