... call, toconnect PBX for call extentions, to connect billing systems for public phone use, to connect VoIP gateway torealize VoIP call ... It can connect with ordinary telephone set, PBX , VOIP Gateway, Billing meter etc. ;3) Dialing tone frequency:450hz;44) SIM card supported ... DTMF Dialing;6) The RJ-11 socket which connect the phone or billing system for metering purpose;7) IP Presetting;8) Working ...