Unlocked GSM smartphones are personal electronic devices. They are designed for use on the most common type of cellular phone network, those that use the Global System for Mobile Communications. The term ‘unlocked’ means the phone is not restricted to the network of a particular cellular provider, but can be configured to work on any network that employs the GSM standard. As smartphones, they are able to act as telephones, but have additional functionality because of their ability to serve as mobile internet access points.
There are several different network standards for cellular communication. Most of the world uses the GSM standard. The United States is the most notable exception to this rule. Some cellular providers in the United States do employ this technology, but it is only one of several network standards in use.
All GSM devices, including unlocked GSM smartphones accept a subscriber identity module card, or SIM card. This small memory card stores information for a phone’s user, and allows that information, and any linked account, to be easily transferred between devices. Often, cell phone service providers will place a hardware or software locking feature in their devices, so that those devices can function on only their network.
Mobile devices may be purchased, generally for a greater fee, without such restrictions. Unlocked GSM smartphones either never had such a lock, or have had it disabled. As a result, they can be freely transferred between networks, will accept any SIM card, and will function normally so long as that SIM card is associated with an active and valid account. Unlocked GSM smartphones are, as a result of this feature, very portable, and allow their users to change carriers easily, without needing to replace their handsets.
Like all smartphones, unlocked GSM smartphones have additional capabilities beyond those available on ordinary handsets. Modern smartphones combine the normal functions of mobile telephones with the features of PDAs. Smartphones also use cellular networks, and often wifi hotspots, to access the Internet.
The functionality of smartphones can also be greatly expanded through the installation of applications, or apps. These small programs take advantage of the internet connectivity, the user's position, and other information provided by the cellular network to offer additional utility to users. Although unlocked GSM smartphones are portable between networks, some apps are proprietary, and not fully portable between different service providers.