Mobile phones are designed to work on cellular networks and contain a standard set of services that allow phones of different types and in different countries to communicate with each other.
Before the phone can be used, a subscription to a mobile phone operator (a.k.a. carrier) is required. The operator will issue a SIM card which contains the unique subscription and authentication parameters for that customer. Once the SIM card is inserted into the phone, services can be accessed. Mobile phones do not only support voice calls; they can also send and receive data and faxes (if a computer is attached), send short messages (or "text messages"; see SMS), access WAP services, and provide full Internet access using technologies such as GPRS. Mobile phones usually have a clock and a calculator and often one can play some games on them.
Many mobile phones support 'auto-roaming', which permits the same phone to be used in multiple countries. For this to work, the operators of both countries must have a roaming agreement.
Newer models also allow for sending and receiving pictures and have a built-in digital camera. This gives rise to some concern about privacy, in view of possible voyeurism, for example in swimming pools. For this reason, Saudi Arabia has entirely banned the sale of camera phones (although the country allows pilgrims on the Hajj to bring in camera phones); South Korea has ordered manufacturers to ensure that all new handsets emit a beep whenever a picture is taken.
GPS receivers are starting to appear in cell phones, primarily to aid in dispatching emergency responders.
Newer models have included many features aimed toward personalisation, such as user defined and downloadable ring tones and logos, and interchangeable covers, which have helped in the uptake by the teenage market. Usually one can choose between a ring tone, a vibrating alert, or a combination of both.
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