... toconnect PBX for call extentions, to connect billing systems for public phone use, to connect VoIP ... torealize VoIP call termination, to connect alarm system for security purpose, etc. It is not ... with ordinary telephone set, PBX , VOIP Gateway, Billing meter etc. ;3) Dialing tone frequency:450hz;44 ... RJ-11 socket which connect the phone or billing system for metering purpose;7) IP Presetting;8) ...