Abstract: Cooperation between two repeater transceivers of a radio trunking system causes a mobile radio transceiver to join or rejoin ongoing communications. To join ongoing communications, a radio transceiver attempts to acquire a free repeater communications channel by transmitting call signalling identifying a group of transceivers to be contacted. If the group to be contacted is already communicating on another repeater communications channel, the calling radio transceiver is forced to leave the communications channel it is trying to acquire and to begin scanning communications channels in search of call signalling identifying it. Meanwhile, the repeater permitting the ongoing communication interrupts the ongoing communications briefly and transmits the call signalling identifying the group of transceivers to be joined (including the radio transceiver which is to join the ongoing communications).