... a GSM to Analog Converter(single port,insert 1 sim card only), the device canproduce a FXS line to ... Billing meter etc. ;3) Dialing tone frequency:450hz;44) SIM card supported (1.8V, 3V);5) DTMF Dialing;6) ... , No.2.in use, No.3, in talk, No.4, Battery, if have, No. 5-7, Signal strengthFront side ... port and switch;Bottom side 1pcs Sim card holder slots, you can insert Sim card into the slot .Accessories:Ac ...