General features

All mobile phones have a number of features in common, but manufacturers also try to differentiate their own products by implementing additional functions to make them more attractive to consumers. This has led to great innovation in mobile phone development over the past 20 years. The common components found on all phones are: All 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. However, they can also support other features added by various manufacturers over the years: roaming which permits the same phone to be used in multiple countries, providing that the operators of both countries have a roaming agreement. send and receive data and faxes (if a computer is attached), access WAP services, and provide full Internet access using technologies such as GPRS. applications like a clock, alarm, calendar and calculator and a few games. Sending and receiving pictures and videos through MMS, and for short distances with e.g. Bluetooth. GPS receivers integrated or connected (i.e. using Bluetooth) to cell phones, primarily to aid in dispatching emergency responders and road tow truck services. This feature is generally referred to as E911. Push to talk, available on some mobile phones, is a feature that allows the user to be heard only while the talk button is held, similar to a walkie-talkie. Global System for Mobile Communications (GSM) services are a standard collection of applications and features available to mobile phone subscribers all over the world. The GSM standards are define

by the 3GPP collaboration and implemented in hardware and software by equipment manufacturers and mobile phone operators. The common standard makes it possible to use the same phones with different companies' services, or even roam into different countries. GSM is the world's most dominant mobile phone standard. The design of the service is moderately complex because it must be able to locate a moving phone anywhere in the world, and accommodate the relatively small battery capacity, limited input/output capabilities, and weak radio transmitters on mobile devices. In wireless telecommunications, roaming is a general term referring to the extension of connectivity service in a location that is different from the home location where the service was registered. Roaming ensures that the wireless device is kept connected to the network, without losing the connection. The term "roaming" originates from the GSM (Global System for Mobile Communications) sphere[citation needed]; the term "roaming" can also be applied to the CDMA technology. Traditional GSM Roaming is defined (cf. GSM Association Permanent Reference Document AA.39) as the ability for a cellular customer to automatically make and receive voice calls, send and receive data, or access other services, including home data services, when travelling outside the geographical coverage area of the home network, by means of using a visited network. This can be done by using a communication terminal or else just by using the subscriber identity in the visited network. Roaming is technically supported by mobility management, authentication, authorization and billing procedures.