A GSM phone is a type of mobile phone that uses the (G)lobal (S)ystem for (M)obile Communications to send and receive phone calls. GSM is a digital standard first offered commercially in 1991 and is currently the most popular mobile phone transmission technology in the world.

The GSM standard uses TDMA digital technology, which allows for three different voice calls to be placed in the same time slot, rather than one call using the old analog "cell" phones. This is possible through digital compression that GSM then builds upon with the addition of encryption. A GSM phone takes up the same amount of transmission space as the old technology, but has the additional benefit of added security.

One of the great benefits of a GSM phone is the addition of a SIM card, or "Subscriber Identification Module." This little chip slips into the back of GSM phones and provides all of the users' personal information. This includes contacts and calendar information in most cases, and more importantly the subscriber's personal identification information. Having this information on removable chip enables a GSM phone user to move a SIM card between mobile phones and still receive voice calls to the same number. It also prevents user from having to re-input personal information each time a new phone is purchased.

In Europe and most of Asia, GSM is the standard used by everyone. Having one technology is great, because users can simply move their chips to different phones if they travel to different countries or in most cases use the same phone. This is in contrast to the US, with so many competing standards and difficulty transferring between carriers.

The adoption of GSM technology and GSM phones as a standard also paved the way for the rise of text messaging in many countries. While text messaging is starting to become popular in North America, it is nowhere near as popular as it is in Europe and Asia. Carriers in the US in particular use various technologies in addition to GSM and must then route text messages through third party gateways. This is how a Sprint user can send a text message to a Verizon customer. Until a few years ago this wasn't possible and served to prevent text messaging from truly catching on.

GSM and GSM phones have found a significant boost due to Cingular Wireless becoming America's largest mobile provider. They have adopted GSM technology and promote the GSM phone's ease of use due to a swappable SIM card. Though the US still has many competing technologies, a GSM phone is the international choice. If you plan to travel frequently overseas, a GSM phone might be the wise decision.