The Global System for Mobile Communications (GSM) is the most popular standard for mobile phones in the world. GSM service is used by over 1.5 billion people across more than 210 countries and territories. The ubiquity of the GSM standard makes international roaming very common between mobile phone operators, enabling subscribers to use their phones in many parts of the world. GSM differs significantly from its predecessors in that both signaling and speech channels are digital, which means that it is considered a second generation (2G) mobile phone system. This fact has also meant that data communication was built into the system from very early on. GSM is an open standard which is currently developed by the 3GPP.

From the point of view of the consumer, the key advantage of GSM systems has been higher digital voice quality and low cost alternatives to making calls such as text messaging. The advantage for network operators has been the ability to deploy equipment from different vendors because the open standard allows easy inter-operability. Also, the standards have allowed network operators to offer roaming services which mean subscribers can use their phone all over the world.

GSM retained backward-compatibility with the original GSM phones as the GSM standard continued to develop, for example packet data capabilities were added in the Release '97 version of the standard, by means of GPRS. Higher speed data transmission have also been introduced with EDGE in the Release '99 version of the standard.