GSM
full spelling ： Global System for Mobile Communications
GSM (Global System for Mobile Communication) is the most widely used standard for mobile phones in the world. GSM was originally developed as a pan-European standard for digital mobile telephones. GSM is one of the main 2G digital wireless standards in many countries throughout the world today.
GSM networks operate in different frequency ranges. Most GSM networks operate in the 900 MHz or 1800 MHz bands. Some countries use the 850 MHz and 1900 MHz frequency bands.