Multimedia group communication over IP is an advanced service gaining growing interest from broadcast, fixed and mobile network operators. Next Generation Networks (NGN) will require that IP based multimedia services to be efficiently delivered to groups over heterogeneous networks with QoS. Although being acknowledged as the most efficient way of delivering group communication in packet switched networks, IP multicast still faces some problems associated with QoS that have limited its success in the past. Furthermore the nonexistence of true multicast in wireless technologies has led to an inefficient mapping between the IP and wireless layers. This paper proposes a technique for efficient dynamic mapping of IP Multicast, optimizing its usage for NGN. This technique is evaluated by a prototype on a WiFi environment.