... dial.5,Lock card, lock terminal.6,Send polarity reversal signal for billing meter while connection.7, ... GPRS . (Optional)9,Rechargeable battery, keep conversation for at least 3 hour when out of mains supply ... . (Optional)10,Transmit tariff for our company phone billing meter. (Optional)Technical Specifications1 ... ,Insertion loss: ≤0.5dB 4 line Wireless Terminal/Fixed wireless terminal