Anysun Goip-16 Gsm Voip Gateway w/ External Antenna 16 GSM Channels up to 16 SIM Cards by GOIP 16 ports 16 sim cards GSM VOIP gateway GOIP Frequency: GSM 850/900/1800/1900MHZ It is ideal for VoIP to Local termination where a fixed telephone line (PSTN) is not available or for cellphone roaming via the a VoIP network. Significant savings on long distance charges can be realized. Open Standard VoIP Protocols (ITU H.323 V4 and IETF SIP V2) Single or Multiple Server Registrations Two 10/100 Ethernet circuits connect to the LAN and an additional device GSM module for making GSM calls