GSM, or Global System for Mobile communications, is the world's most popular wireless technology for cellular devices. As of 2014, GSM is used by over 80 percent of the world, or nearly 3 billion people.
Development on GSM began in 1982 by the Groupe Spécial Mobile committee. In comparison to its predecessors, GSM features digital signaling and speech channels, which allow for data transmissions to be built into GSM alongside standard voice communication. The cell phone carriers T-Mobile and AT&T utilize GSM technology in their networks, while competing carriers Sprint, Virgin Mobile and Verizon Wireless use a similar technology called Code Division Multiple Access, or CDMA.
CDMA networks support a wider bandwidth by spreading electromagnetic energy. With CDMA, multiple cell phone users can share the same communication channel at the same time. CDMA also allows more space to be allocated for data, which has increased its usage for high-speed data communication.
Compared to CDMA, GSM carriers typically have roaming contracts with other GSM carriers, allowing for a greater coverage area. In addition, GSM-compatible cell phones utilize Subscriber Identity Module (SIM) cards, which can be swapped out of the phone for a SIM card from another GSM carrier. This allows for the cell phone user to change carriers without the need to purchase a new phone.