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A mobile phone (also known as a wireless phone or cellular phone ) is a short-range, electronic device used for mobile voice or data communication over a network of specialised base stations known as cell sites. In addition to the standard voice function of a mobile phone, telephone, current mobile phones may support many additional services, and accessories, such as SMS for text messaging, email, packet switching for access to the Internet, gaming, bluetooth, infrared, camera with video recorder and MMS for sending and receiving photos and video. Most current mobile phones connect to a cellular network of base stations (cell sites), which is in turn interconnected to the public switched telephone network (PSTN) (the exception is satellite phones).

Overview

According to internal memos, American Telephone & Telegraph discussed developing a wireless phone in 1915, but were afraid deployment of the technology could undermine its monopoly on wired service in the U.S.

The first commercial mobile phone service was launched in Japan by NTT in 1978. By November 2007, the total number of mobile phone subscriptions in the world had reached 3.3 billion, or half of the human population (although some users have multiple subscriptions, or inactive subscriptions), which also makes the mobile phone the most widely spread technology and the most common electronic device in the world.

The first mobile phone to enable internet connectivity and wireless email, the Nokia Communicator, was released in 1996, creating a new category of multi-use devices called smartphones. In 1999 the first mobile internet service was launched by NTT DoCoMo in Japan under the i-Mode service. By 2007 over 798 million people around the world accessed the internet or equivalent mobile internet services such as WAP and i-Mode at least occasionally using a mobile phone rather than a personal computer.

Cellular systems

Mobile phones send and receive radio signals with any number of cell site base stations fitted with microwave antennas. These sites are usually mounted on a tower, pole or building, located throughout populated areas, then connected to a cabled communication network and switching system. The phones have a low-power transceiver that transmits voice and data to the nearest cell sites, normally not more than 8 to 13 km (approximately 5 to 8 miles) away.

When the mobile phone or data device is turned on, it registers with the mobile telephone exchange, or switch, with its unique identifiers, and can then be alerted by the mobile switch when there is an incoming telephone call. The handset constantly listens for the strongest signal being received from the surrounding base stations, and is able to switch seamlessly between sites. As the user moves around the network, the "handoffs" are performed to allow the device to switch sites without interrupting the call.

Cell sites have relatively low-power (often only one or two watts) radio transmitters which broadcast their presence and relay communications between the mobile handsets and the switch. The switch in turn connects the call to another subscriber of the same wireless service provider or to the public telephone network, which includes the networks of other wireless carriers. Many of these sites are camouflaged to blend with existing environments, particularly in scenic areas.

The dialogue between the handset and the cell site is a stream of digital data that includes digitised audio (except for the first generation analog networks). The technology that achieves this depends on the system which the mobile phone operator has adopted. The technologies are grouped by generation. The first-generation systems started in 1979 with Japan, are all analog and include AMPS and NMT. Second-generation systems, started in 1991 in Finland, are all digital and include GSM, CDMA and TDMA.

The nature of cellular technology renders many phones vulnerable to 'cloning': anytime a cell phone moves out of coverage (for example, in a road tunnel), when the signal is re-established, the phone sends out a 're-connect' signal to the nearest cell-tower, identifying itself and signalling that it is again ready to transmit. With the proper equipment, it's possible to intercept the re-connect signal and encode the data it contains into a 'blank' phone -- in all respects, the 'blank' is then an exact duplicate of the real phone and any calls made on the 'clone' will be charged to the original account.

Third-generation (3G) networks, which are still being deployed, began in Japan in 2001. They are all digital, and offer high-speed data access in addition to voice services and include W-CDMA (known also as UMTS), and CDMA2000 EV-DO. China will launch a third generation technology on the TD-SCDMA standard. Operators use a mix of predesignated frequency bands determined by the network requirements and local regulations.

In an effort to limit the potential harm from having a transmitter close to the user's body, the first fixed/mobile cellular phones that had a separate transmitter, vehicle-mounted antenna, and handset (known as car phones and bag phones ) were limited to a maximum 3 watts Effective Radiated Power. Modern handheld cellphones which must have the transmission antenna held inches from the user's skull are limited to a maximum transmission power of 0.6 watts ERP. Regardless of the potential biological effects, the reduced transmission range of modern handheld phones limits their usefulness in rural locations as compared to car/bag phones, and handhelds require that cell towers be spaced much closer together to compensate for their lack of transmission power.

Some handhelds include an optional auxiliary antenna port on the back of the phone, which allows it to be connected to a large external antenna and a 3 watt cellular booster. Alternately in fringe-reception areas, a cellular repeater may be used, which uses a long distance high-gain dish antenna or yagi antenna to communicate with a cell tower far outside of normal range, and a repeater to rebroadcast on a small short-range local antenna that allows any cellphone within a few meters to function properly.

Handsets

Nokia is currently the world's largest manufacturer of mobile phones, with a global device market share of approximately 40% in 2008. Other major mobile phone manufacturers (in order of market share) include Samsung (14%), Motorola (14%), Sony Ericsson (9%) and LG (7%). These manufacturers account for over 80% of all mobile phones sold and produce phones for sale in most countries.

Other manufacturers include Apple Inc., Audiovox (now UTStarcom), Benefon, BenQ-Siemens, CECT, High Tech Computer Corporation (HTC), Fujitsu, Kyocera, Mitsubishi Electric, NEC, Neonode, Panasonic (Matsushita Electric), Pantech Curitel, Philips, Research In Motion, Sagem, Sanyo, Sharp, Siemens, Sendo, Sierra Wireless, SK Teletech, Sonim Technologies, T&A Alcatel, Huawei, Trium and Toshiba. There are also specialist communication systems related to (but distinct from) mobile phones.

There are several categories of mobile phones, from basic phones to feature phones such as musicphones and cameraphones, to smartphones. The first smartphone was the Nokia 9000 Communicator in 1996 which incorporated PDA functionality to the basic mobile phone at the time. As miniaturisation and increased processing power of microchips has enabled ever more features to be added to phones, the concept of the smartphone has evolved, and what was a high-end smartphone five years ago, is a standard phone today. Several phone series have been introduced to address a given market segment, such as the RIM Blackberry focusing on enterprise/corporate customer email needs; the SonyEricsson Walkman series of musicphones and Cybershot series of cameraphones; the Nokia N-Series of multimedia phones; and the Apple iPhone which provides full-featured web access and multimedia capabilities.

Features

Mobile phones often have features beyond sending text messages and making voice calls, including Internet browsing, music (MP3) playback, memo recording, personal organiser functions, e-mail, instant messaging, built-in cameras and camcorders, ringtones, games, radio, Push-to-Talk (PTT), infrared and Bluetooth connectivity, call registers, ability to watch streaming video or download video for later viewing, video calling and serve as a wireless modem for a PC, and soon will also serve as a console of sorts to online games and other high quality games. The total value of mobile data services exceeds the value of paid services on the Internet, and was worth 31 billion dollars in 2006 (source Informa). The largest categories of mobile services are music, picture downloads, videogaming, adult entertainment, gambling, video/TV.

Nokia and the University of Cambridge are showing off a bendable cell phone called Morph .

Applications

The most commonly used data application on mobile phones is SMS text messaging, with 74% of all mobile phone users as active users (over 2.4 billion out of 3.3 billion total subscr

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First of all, if you happen to travel overseas on a regular basis, you can go on with the buying of SIM cards; that too, prepaid, in the country that you’re in. It could be used immediately with an unlocked cell phone of yours.

If you intend on purchasing a new-fangled cell phone, it would be better to go for a new unlocked cell phone. Most of the people, upon listening to this piece of advice, wonder why to go for unlocked phone?

party_lik3_a_r0ck_star asks: "Do unlocked cell phones work with cingular prepaid services?"

yachi replies: 'Yes, any unlocked phone bought in the United States will work with Cingular service.'

Charlie P replies: 'yes any unlocked GSM will work with cingular prepaid'

Peter I replies: 'any unlock phones will work'

Walter M asks: "Can someone please help me telling me the best websites to fin cheap and unlocked cell phones?? Thanks in advance!"

matt.basically replies: 'tryand find your city. then click on electronics.you can usually find some on there, and you may not have to pay shipping. :-)'

Elena asks: "I always find unlocked cell phones that I want to buy but I have Sprint. I know you can use unlocked cell phones with other carriers but I'm not sure if it will work with Sprint cause they don't use sim cards."

Zendoo replies: 'It depends on the network that the phone operates on. Typically "Unlocked" refers to a GSM phone that is not SIM Locked to a specific carrier. If the phone is GSM, you will need a SIM Card to operate it, which means it is not compatible with SPRINT. If the phone is an unlocked CDMA network phone, you should not have a problem.If the reason you are looking for an unlocked phone is that you want to upgrade your phone without changing your contract I would suggest buying a used SPRINT phone and transferring your phone number. You can find thousands of unlocked phones and used SPRINT phones online at'

z_marcot asks: "what does an unlocked cell phone do that a locked one doesn't?Are unlocked cell phones illegal? and if so were."

Cassandra Estell replies: 'Locked phones are phones which only allow you to use the network sim that you were supplied with ie T-Mobile phones are locked to the T-mobile network so you can only use their sim cards, not an Orange one.If you get your handset from Carphone Warehouse or O2 these phones come already unlocked (O2 wont tell you this).Getting a handset unlocked so you can use any sim brand is perfectly legal. The network provider can do it and so can most mobile phone repair shops (the repair shops are cheaper).So an unlocked phone allows you to use many different network sims.'

Alex G replies: 'Difference if the fact that a locked cellphone will only work on a specific network. Once you unlock it you can change the network'

robertminidriver asks: "Can I buy an unlocked phone and then get it activated by my cell phone company without the company forcing me to change or upgrade my current plan?"

Paultech replies: 'or all u would need to do is get a new sim for the phone. which u can get from most phone shops if u want to go pay as u go. if u want to go contract then there might be a few problems with that.'

coolbeanie27 replies: 'Yes if the cell phone is unlocked, That means for example you have cell service with us cellular and the phone you bought is a t-mobile phone but it is unlocked. You take your phone to us cellular and they can obtain a number that you program into your t-mobile phone and it will allow you to use it with your us cellular service.If the phone is the same provider as your current service then just put your sims card into it and it will work.'

weebles replies: 'Some companies such as Cingular lock their phones so if you buy a phone from them you can't use it except with them. Unlocked phones can be used with any company that uses the same technology. for example nextel will only work with IDEN tech and verizon, sprint, US Cellular will only work with CDMA, TMobile, Cingular, CellularONE will only work with GSM. know what you are buying and what you need before you get it.'

Serious Black replies: 'You can buy an unlocked cell phone but you should conduct some research/web search prior to purchasing it. You have to make sure that the technologies are compatable, i.e the phone you want and the service you have currently - - 3G, CDMA, GSM, EV-DO, etc.The other thing to take in to consideration is that some of the features on the phone you want might have software/features that are compatable with that of the ORIGINAL carrier the phone was UNlocked from. Those features might be the ability to download ringtones, wallpapers, animations and games.DO YOUR RESEARCH BEFORE YOU MAKE YOUR PURCHASE.'

bill91173 replies: 'There are actually a couple questions here. Unlocked phones as explained in some of the other answers refers to not having a "subsidy lock". A "subsidy lock" means that the wireless provider has had the equipment locked to their network in an effort to minimize financial loss when providing phones at a significantly discounted price or sometimes for free with a new contract. If you have an unlocked phone of the correct technology you can get it activated. The second part about not changing your plan will depend on a few things. Primarily if your old phone is the same technology or not. Changing phone technology will frequently require changing rate plans. If both old phone and new phone are the same technology you should be able to switch phones. Be sure to notify your provider so they can note the new phone's identification (IMEI) in their system. That will help confirm that data services will work correctly and if you carry insurance on your phone you can make sure the right phone is insured.'

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