The SIM card is approximately the size of a small postage stamp and is usually placed underneath the battery in the rear of the unit. The SIM securely stores the service-subscriber key IMSI used to identify a subscriber on mobile telephony devices such as mobile phones and computers. The SIM card allows users to change phones by simply removing the SIM card from one mobile phone and inserting it into another mobile phone or broadband telephony device. A SIM card contains its unique serial number, internationally unique number of the mobile user IMSIsecurity authentication and ciphering information, temporary information related to the local network, a list of the services the user has access to and two passwords PIN for usual use and PUK for unlocking.
History[ change change source ] Mobile phones in the s through s were large and heavy, and most were built into cars. In the late 20th century technology improved so people could carry their phones easily.
Martin Cooper from Motorola made the first call using a mobile phone init did not use the type of cellular mobile phone network that we use today.
The first mobile phone networks were created in the late s in Japan. Now almost all urban areas, and many country areas, are covered by mobile phone networks. Inside a mobile phone Technology[ change change source ] A cell phone combines technologies, mainly telephone, radioand computer.
Most also have a digital camera inside. Cell phones work as two-way radios. They send electromagnetic microwaves from base station to base station. The waves are sent through antennas.
This is called wireless communication. Early cell telephones used analog networks. They became rare late in the 20th century. Modern phones use digital networks. The first digital networks are also known as second generation, or 2G, technologies. The difference is in communication protocol.
Other countries like Japan have different 2G protocols.
A few 2G networks are still used. The radio waves that the mobile phone networks use are split into different frequencies. The frequency is measured in Hz.
Low frequencies can send the signal farther. Higher frequencies provide better connections and the voice communications are generally clearer. Four main frequencies are used around the world: Today there are mobile phones that work on two, three or four frequencies.
The most advanced phones work on all frequencies.Uses The ability to communicate wirelessly and across borders is one of the biggest uses of mobile phones. Mobile phones have emerged as the primary communication devices for millions of rural, remote and underdeveloped areas in developing countries where it is difficult to build extensive fixed-line and other wired phone infrastructures.
Mobile phones in the classroom: teachers share their tips From multimedia to geocaching, the possibilities for using mobiles to engage learners are endless.
Many use their mobiles to record. A mobile phone, known as a cell phone in North America or hand phone in Asian English, is a portable telephone that can make and receive calls over a radio frequency link while the user is moving within a telephone service area.
List of countries by number of mobile phones in use This list ranks the countries of the world by the number of mobile phones in use.
Note that it is not the number of phone devices that are being given here, but the number of phone numbers in a country.
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