... +GSM FWT. VOIP+GSM gateway. IMEI change,VPN PPTP,Encryption.Quad band,GOIP VOIP GSM gatewayGoIP4 GSM Gateway bridges the GSM and ... a fixed telephone line (PSTN) is not available or for cellphone roaming via the a VoIP network. Significant savings on long ... /µ law), G.729A/B, G.723.1DTMF: RFC 2833, In-band DTMF, SIP INFOPhysical and EnvironmentalOperating temperature: 10°C to 40 ...