A system and method for optimizing call setup latency for geographically dense groups including updating client location information using at least one application server while the client moves from one sector to another to provide a location update; identifying and updating parameters including location update information uniquely identifying a sector from which a client is receiving communication service; and determining at least one geographically dense call group; and choosing at least one designated responder to the at least call group. A client per cluster is selected as a designated responder for that cluster and when the server needs to set up a geographically dense group call, a random number is included corresponding to the designated responder for that group in a call setup message.