A method and system for completing a call between a first mobile device located at a first communication system and a second mobile device located at a second communication system is provided. A call initiation request including a request to complete a call with the second mobile device is received at a Radio Access Network (RAN) Adaptor (RA) from the first mobile device. The RA determines RAN-specific access parameters for the first mobile device and the second mobile device. The RA sends a call processing call initiation request including the RAN-specific access parameters and call initiation information for the first mobile device and the second mobile device to a cloud-based group call service. The RA establishes resources specific to the RAN in the RA. The resources include first resources at the first communication system and second resources at the second communication system. The call between the first mobile device and the second mobile device is completed using the first resources and the second resources.