GSM (Global System for Mobile communications) is an open, digital cellular technology used for transmitting mobile voice and data services that is widely used in Europe and other parts of the world. GSM differs from first generation wireless systems in that it uses digital technology and Time Division Multiple Access (TDMA) transmission methods. GSM is a circuit-switched system that divides each 200 kHz channel into eight 25kHz time-slots. GSM operates between 850 MHz and 1.9 GHz in more 210 countries. The GSM standard has given birth to wireless services like General Packet Radio Service (GPRS) and Enhanced Data Rates for GSM Evolution (EDGE). Its end users were the first to take advantage of an inexpensive implementation of SMS (short message system), which is more popularly known as texting. One of the main advantages of the GSM standard is the ability to roam and switch carriers by using individual mobile units (if partner networks are located in their destination).