SIM lock
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A SIM lock is a feature implemented by mobile phone manufacturers and providers to allow only the use of SIM cards in the phone that meet specific criteria. Currently, phones can be locked to only accept SIM cards from one or more of the following:
- Countries
- Networks (e.g. T-Mobile, Orange, etc)
- Providers
- SIM types (i.e. only specific SIM cards can be used with the phone).
A SIM lock is typically applied on a mobile phone that is supplied to a customer on favorable conditions, such as a phone provided without charge on a contract.
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Types of SIM locks
The country lock only allows the use of the phone with SIM cards that originated in a specific country or group of countries.
A network lock only allows the use of the phone with specific networks.
The most restrictive type of lock which can be used is the full SIM card lock, which means that a phone will only work with one SIM card. If that SIM card malfunctions or is damaged, the phone will no longer work and must be serviced.
Laws on SIM locking
Numerous countries have laws prohibiting SIM locking, for example Finland, while in countries such as Hungary, all phones are SIM-locked for life, and unlocking them is prohibited.
Most fall somewhere in between, allowing locking, but only for the duration of the customer's current service contract. At this time it is either mandatory or voluntary for the provider to unlock the customer's mobile phone. However, some providers, including the former AT&T Wireless, never unlock handsets, even after a customer has fulfilled their service contract. Other providers, for example T-Mobile and more recently Cingular will unlock phones if the customer has an active account in good standing for at least 90 days.
Unlocking
A handset can be unlocked by entering a special code, or in some cases, over-the-air by the carrier.
The code required to remove all SIM locks from a phone is called the master code or network code key. In the past, it was generated using a mathematical formula, usually based on the phone's unique IMEI or MCC codes. However, this became too easy to break, and, nowadays, the unlock codes are generated randomly and retained by the provider.
Typically, a locked phone will display a message if a restricted SIM is used, requesting the unlock code. In some cases, the phone will simply display a message explaining that it is locked. This is especially the case with handsets provided by Cingular Wireless.
For example, on the Sony Ericsson T610 mobile phone, "Insert correct SIM card" will appear on the phone's LCD display if the wrong SIM is used. Once a valid unlocking code is entered, the phone will display "Network unlocked".
Unlocking via computer
One of the most popular ways phones are unlocked is using the RS-232 or LPT port of a computer using software usually written specifically for the model of phone being unlocked. In some cases, special "phone clips" are used which re-program the software that controls the phone, removing the SIM lock. However, such clips are usually very expensive.
Regulations on unlocking
Unlocking a phone without the permission or unlocking code from the provider is usually in breach of the agreement with the provider, though most countries do not make specific laws prohibiting the removal of SIM locks. For example, in Poland, the law states that providers cannot word their customer contracts so that they forbid the removal of SIM locks, and the process is entirely legal providing that the IMEI number of the phone is not changed during the unlocking process.
In the United Kingdom, there are also no specific laws that prohibit unlocking, however, under the Mobile Telephones (Re-programming) Act, changing the IMEI of the phone is illegal.
Related links
- A site offering instant worldwide mobile phone unlocking for $1.99 (http://www.uniquephones.com)