Specifications:  GSM 850/900/1800/1900MHZ Can lock card, lock terminal Support polar-reverse, 12 or 16kHz pulse signal, GPRS Suitable for connecting with the payphone GSM cellular network outgoing GSM cellular network incoming DTMF caller ID Support secondary dial Send 16kHz pulse for billing meter while connection Send polarity reversal signal for billing meter while connection RS-232 Interface perform wireless GPRS cooperate with PC (optional) Rechargeable battery, keep conversation for at least 2 hour when out of mains supply (optional) Technical Specifications Work frequency: GSM 900MHZ/1800MHZ or GSM 850/900/1800/1900MHZ Power: 2 W Sensitivity: -104dB Power consumption: Static 25mA, Transmit600mA Ambient noise: 60dB Power Supply: DC 5Vadapter AC 110~240 input DTMF Receive: > -23dB insure receiving. DTMF Receive sensitivity: 99.99% Insertion loss: 0.5dB