The leading phone system manufacturers including Avaya, Siemens and Panasonic are now providing VoIP solutions that use a mix of PSTN, ISDN and VoIP technology. There is also a growing trent towards SIP based PBX systems that increasingly rely on using SIP trunks for making calls. Our range of VoIP GSM Gateways and SIP GSM Fixed Cellular Terminals cater for this need to communicate with GSM networks using the latest SIP trunk interfaces.