The invention relates to a system for controlling communication between user terminals using a telecommunications network. One embodiment includes an interface between a real-time charging control system for controlling usage of network resources during such usage and a group communications control node which is capable of controlling group communications sessions. Improved real-time charging control mechanisms can be implemented to account for usage of group communications services, for example where charging for an entire group communications session may be applied to a selected single party. Charging for a group communications session may be conducted with the flexibility of being able to charge according to the number of participants without having to transmit separate charging control signals from each participant's leg of the session to the real-time charging control system, thus reducing the signaling load in the network.