The GSM business telephone follows the usage of ordinary of telephone while it contains the communication functions of a handset. With built-in charging system, there is no need to buy an external one, thus saves money. It solves communication interruptions caused by voltage fluctuation and power down problems through using backup Li-Ni battery. This product has been widely used both at home and abroad thanks to its powerful functions and easy operations. Features: 1) Industrial GSM module 2) Menu in English and Chinese 3) Voice volume adjustable 4) Built-in charging system 5) Internal Li-Ni backup battery 6) Support English and Chinese SMS 7) Display of dialing calls, incoming calls and missed calls 8) Preset local handset numbers and block numbers 9) Locking network, SIM card, and machine and card together 10) Preset local prefix and IP access number 11) GPRS wireless online Specifications: 1) Frequency: GSM900 / 1,800 / 1,900MHz 2) Power supply: 110 ~ 240V AC, 7V DC 50/60Hz 3) Temperatures: -10°C ~ +50°C 4) Humidity: 10% ~ 95% 5) Pressures: 86 ~ 106KPa