Guide to GSM - What's the fuss about ?
GSM handsets use a Subscriber Identity Module (SIM) smart card, which contains user account information as well as additional storage for personalized user data (phonebooks, etc.). A GSM phone is immediately programmed upon insertion of a SIM card, thus allowing GSM phones to be easily rented, borrowed or exchanged. SIM cards can be programmed to display custom menus for personalized services. GSM provides a short messaging service (SMS) that enables text messages up to 160 characters in length to be sent to and from a GSM phone.
GSM together with other technologies is part of an evolution of wireless mobile telecommunication that includes High-Speed Circuit-Switched Data (HCSD), General Packet Radio System (GPRS), Enhanced Data GSM Environment (EDGE), and Universal Mobile Telecommunications Service (UMTS)