A wireless communication system 200 comprises a connectionless packet network 201 coupled to a plurality of sites 203-208 that are in wireless communication with a plurality of subscriber units 210-217 logically arranged into a plurality of talk groups having corresponding talk group identifications. In one embodiment, each site maintains mappings 220-225 of at least one multicast address to at least one talk group identification. In another embodiment, individual subscriber units maintain such mappings 320. When a subscriber unit affiliates with a given site and talk group (501, 601), the site identifies a multicast address corresponding to the talk group. Based on the multicast address, the site can participate in traffic targeted for the multicast address and, consequently, for the talk group. In this manner, mobility Processing is decentralized, system calability is improved and call setup delays are minimized.