GSM is a cellular network, which means that cellular phones connect to it by searching for cells in the immediate vicinity. GSM networks operate in four different frequency ranges. Most GSM networks operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas including Canada and the United States use the 850 MHz and 1900 MHz bands because the 900 and 1800 MHz frequency bands were already allocated.
Global System for Mobile communications (GSM: originally from Groupe Spécial Mobile) is the most popular standard for cell phones in the world. GSM Association (GSM promoter), estimate that 82% of the global cellular phone market uses the standard. GSM is used by over 2 billion people across more than 212 countries and territories. Its ubiquity makes international roaming very common between cellular phone operators, enabling subscribers to use their phones in many parts of the world. GSM differs from its predecessors in that both signaling and speech channels are digital call quality, and so is considered a second generation (2G) cell phone system. This has also meant that data communication were built into the system using the 3rd Generation Partnership Project (3GPP).
The key advantage of GSM systems to consumers has been better voice quality and low-cost alternatives to making calls, such as the Short message service (SMS, also called "text messaging"). The advantage for network operators has been the ease of deploying equipment from any vendors that implement the standard. Like other cellular standards, GSM allows network operators to offer roaming services so that subscribers can use their phones on GSM networks all over the world.Subscribers can also buy an Unlocked Gsm Cell Phone and use it any where in the world. All that is needed is prepaid SIM card which can be purchased at any cell phone store.
Newer versions of the standard were backward-compatible with the original GSM phones. For example, Release '97 of the standard added packet data capabilities, by means of General Packet Radio Service (GPRS). Release '99 introduced higher speed data transmission using Enhanced Data Rates for GSM Evolution (EDGE).