The disclosure is related to group communications over multicast services. A user equipment (UE) sends a registration request to a server, the registration request indicating communications group(s) in which the UE is interested, receives a message indicating a set of the communications groups that have been assigned pre-established multicast resources, receives call identifiers, the call identifiers mapped to group identifiers of each communications group in the set of the communications groups, stores a mapping of the call identifiers to the group identifiers, and maintains group call sessions for the set of the communications groups. The server receives the registration request, determines that the UE is provisioned for pre-established group calls, retrieves group identifiers for the communications groups, maps call identifiers to the group identifiers, notifies the UE of the set of the communications groups and the mapped call identifiers, and assigns multiple group calls onto pre-established multicast resources.