GSM (Global System for Mobile Communications: originally from Groupe Spécial Mobile) is the most popular standard for mobile telephone systems in the world.
GSM World - Online face of GSM Association - "The GSMA represents the interests of the worldwide mobile communications industry"
The GSM Association, its promoting industry trade organization of mobile phone carriers and manufacturers, estimates that 80% of the global mobile market uses the standard. GSM is used by over 3 billion people across more than 212 countries and territories. - GSM Wiki
GSM Technology for Mobile Communications
EDGE - GSM Evolution (EDGE) technology provides up to three times the data capacity of GPRS
HSPA - The set of technologies that defines the migration path for 3G/WCDMA operators worldwide
GSM - An open, digital cellular technology used for transmitting mobile voice and data services
GPRS - A very widely deployed wireless data service, available now with most GSM networks