1.General description Gsm fwt-8848 is a gsm to analog converter(single port, insert 1 sim card only), the device can produce a fxs line to allow a regular phone to be connected and used just like a local landline(pstn) except your calls will go out the gsm network. This device can both receive and make calls. The main application is: connecting the rj-11 fxs line to connect ordinary telephone set for voice call; to connect pbx for call extensions; to connect billing systems for public phone use; to connect voip fxo gateway to realize voip call termination; to connect alarm system for security purpose, etc. It is not a voip gateway, nor a gsm+voip gateway, it is a gsm fixed wireless terminal that produces an analog fxs phone line . 2.Features: 1)frequency:gsm 900/1800mhz or gsm 850/900/1800/1900mhz 2) it is a 1 channel gsm gateway which has 2 rj-11 outputs for extensions; 3) it can connect with ordinary telephone set, pbx , voip gateway, billing meter etc. ; 4) dialing tone frequency:450hz; 5) employ industrial module to make; 6) can adjust dial interval from 0.5sec to 9 secs by setting up from telephone set; 7) can adjust voice volume by setting up from telephone set; 8) sim card supported (1.8v, 3v); 9) caller id display; 10) dtmf dialing; 11) bell signal; 12) polarity reversal; 13) the rj-11 socket which connect the phone or billing system for metering purpose; 14) antenna socket (sma); 15) ip presetting; 16) working status and signal strength by led indicator; 17) imei change (optional). 18) back up li-ion battery( optional) 7.2v 1300mah.Standby 24hrs, talking time: 2.5hrs.