Mobile Phone Parts, SIM cards and Mobile Phone unlocking
Mobile Phone - also known as a Cell Phone
A mobile phone or mobile (also called cellphone and handphone, as well as cell phone, wireless phone, cellular phone, cellular device, cell, cellular telephone, mobile telephone or cell telephone) is a long-range, electronic device used for mobile telecommunications (mobile telephony, text messaging or data transmission) over a cellular network of specialized base stations known as cell sites.
Most current mobile phones connect to a cellular network consisting of switching points and base stations (cell sites) owned by a mobile network operator (the exception is satellite phones, which are mobile but not cellular). In addition to the standard voice function, 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, MP3 player, radio and GPS.
As opposed to a radio telephone, a mobile phone offers full duplex communication, automatised calling to and paging from a public switched telephone network (PSTN), and handoff (American English)/handover (British/European English) during a phone call when the user moves from one cell (base station coverage area) to another. A mobile phone offers wide area service, and should not be confused with a cordless telephone, which also is a wireless phone, but only offer telephony service within a limited range, e.g. within a home or an office, through a fixed line and a base station owned by the subscriber.
The International Telecommunication Union estimated that mobile cellular subscriptions worldwide would reach approximately 4.1 billion by the end of 2008. Mobile phones have gained increased importance in the sector of Information and communication technologies for development in the 2000s and have effectively started to reach the bottom of the economic pyramid.
SIM Card
A subscriber identity module (SIM) on a removable SIM card 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 (IMSI), security 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).
SIM cards are available in three standard sizes. The first is the size of a credit card (85.60 mm × 53.98 mm x 0.76 mm). The newer, most popular miniature version has the same thickness but a length of 25 mm and a width of 15 mm, and has one of its corners truncated (chamfered) to prevent misinsertion. The newest incarnation known as the 3FF or micro-SIM has dimensions of 15 mm × 12 mm. Most cards of the two smaller sizes are supplied as a full-sized card with the smaller card held in place by a few plastic links; it can easily be broken off to be used in a device that uses the smaller SIM.
The first SIM card was made in 1991, with Munich smart card maker Giesecke & Devrient selling the first 300 SIM cards to Finnish wireless network operator Radiolinja.
Unlocking
On some networks, the mobile phone is locked to its Carrier SIM card e.g. on the GSM networks in the USA and the UK. This tends to happen only in countries where mobile phones are heavily subsidised, but even then not all countries and not all operators. In the US the phones are locked to the carrier, meaning that only specific carriers' SIM cards will work. In the UK, typically, most phones with subsidies are SIM-locked.
Phones sold with a contract are often locked (SIM-locked) to the network that provided the phone, since the phones are often subsidized in return for using provider for a minimum term (typically, 12 or 24 months). For example in the UK, a phone that would cost £250 without a contract might be offered free-of-charge with an 18 month contract commitment of £30 per month (£540 commitment in total).
A plethora of online and high-street (third-party) businesses now offer the ability to remove the SIM-lock from a phone, effectively making it possible to then use the phone on any network by inserting a different SIM card. This is a useful benefit for travellers that might want to put a local SIM card into their phone when they arrive in a country, in order to minimize roaming charges. In many countries, now it is possible to buy a pre-pay SIM card just by walking into a store, and these SIM-only deals are a cost effective way to stay in contact when travelling.