A wireless communication system 200 comprises a connectionless packet network 201 coupled to a plurality of sites 203–208. Upon a first communication unit (213) initiating a call request for a 2-party call with a second communication unit (215), a call server 235 identifies respective multicast IP addresses (MC1, MC2) associated with the source and target. If the first communication unit 213, or its associated site (205) desires to send payload to the second communication unit 215, it addresses the payload to the multicast IP address (MC2) of the second communication unit, and the second communication unit 215, or its associated site 206 joins the multicast address MC2 to receive the payload. Conversely, if the second communication unit 215, or its associated site (206) desires to send payload to the first communication unit 213, it addresses the payload to the multicast IP address (MC1) of the first communication unit, and the first communication unit 213, or its associated site 205 joins the multicast address MC1 to receive the payload.