Method and apparatus for data packet communications in a communication system. Packets are received at a gateway having an Internet Protocol (IP) destination address and Network Access Identifier (NAI). The gateway maps the received NAI to a local network, such as supported by a Network Address Translator (NAT). The gateway then converts the destination address to a NAT address of the local network. The gateway also adds a port number that allows the NAT to identify the target recipient. The mapping within the gateway is created and maintained as Mobile Stations send registration requests upon arrival within a local network. In one embodiment, the registration request is a Session Initiation Protocol (SIP) registration.