The Telecom FM OneStream VoIP GSM gateway is ideal for use as a SIP trunk device for use with VoIP Telephone Systems for calls to the GSM mobile phone network. The Telecom FM OneStream SIP unit will ideally be used as a SIP Trunk unit for any SIP based Voice Over IP Telephone System. The unit will use 2 SIM cards for 2 simultaneous calls and will also be able to connect to 2 x PSTN telephone lines and support Least Cost Routing between the GSM and PSTN network. The Telecom FM OneStream VoIP GSM Gateway also supports H.323 VoIP.