A SIM lock , simlock , network lock or subsidy lock is a capability built into GSM phones by mobile phone manufacturers. Network providers use this capability to restrict the use of these phones to specific countries and network providers. Generally, phones can be locked to accept only SIM cards based on the International Mobile Subscriber Identity, which has elements of:
- Mobile country code (MCC; e.g., will only work with SIMs issued in one country)
- Mobile network code (MNC; e.g., AT&T Mobility, T-Mobile, Vodafone, etc.)
- Mobile station identification number (MSIN; i.e., only one SIM can be used with the phone)
Additionally, at least Nokia phones can lock group IDs which are used in voice group call service.
In most countries, most mobile phones are shipped with country and/or network provider locks. In addition, these locked phones tend to have firmware installed on them which is specific to the network provider. For example, if you have a Vodafone or Telstra branded phone in Australia, it displays the relevant logo and may only support features provided by that network (e.g., Vodafone Live!). This firmware is installed by the service provider and is separate from the locking mechanism.
Most mobile phones can be unlocked to work with any GSM, such as O 2 or Orange (in the UK), but the phone may still display the original branding and may not support features of the new carrier. Most phones can be unbranded by uploading a different firmware version, a procedure recommended for advanced users only.
Unlocking technology
A handset can be unlocked by entering a special code, or in some cases, over-the-air by the carrier. Usually the unlock process is permanent. One example where it is not is the Apple iPhone, which is officially unlocked (when applicable) every time during its activation step. The code required to remove all SIM locks from a phone is referred to as the master code , network code key , multilock code .
Typically, a locked phone will display a message if a restricted SIM is used, requesting the unlock code. For example, on the Sony Ericsson T610 mobile phone, "Insert correct SIM card" will appear on the phone's display if the wrong SIM is used. Once a valid unlocking code is entered, the phone will display "Network unlocked". In some cases, the phone will simply display a message explaining that it is locked. This is especially the case with handsets provided by AT&T Mobility.
The unlock code is verified by the phone itself, and is either stored in a database or calculated using an obscure mathematical formula by the provider. The algorithms used in earlier Nokia brand phones (based on IMEI and MCC code) have been reverse engineered, stolen or leaked, resulting in many people offering Nokia unlock codes for free or for a fee. Newer Nokia phones have more robust encoding algorithms and permit fewer attempts at unlocking and are not unlockable by these free unlocking programs.
Many other manufacturers have taken a more cautious approach, and embed a random number in the handset's firmware that is only retained by the network on whose behalf the lock was applied. Such phones can often still be unlocked, but need to be connected to special test equipment that will rewrite that part of its firmware where the lock status is kept.
Most phones have security measures built in their software that prevent users from entering the unlock code too many times. After that the phone becomes "hard-locked" and special unlocking equipment has to be used in order to unlock it.
Handset manufacturers have economic incentives both to strengthen SIM lock security (which placates network providers and enables exclusivity deals), but also to weaken it (broadening a handset's appeal to customers who are not interested in the service provider that offers it). Also, making it too difficult to unlock a handset makes it less appealing to network service providers that have a legal obligation to provide unlock codes for every handset they've ever sold.
The main reason to unlock a phone is to be able to use it with a different SIM card. For example, when traveling abroad it's usually cheaper to temporarily use a foreign network, for example with a prepaid subscription. An unlocked phone can't access extra cell phone towers or give free phone service. All it can do is accept other SIMs.
In some cases, a SIM locked handset is sold at a substantially lower price than an unlocked one, because the service provider expects income through its service. A consumer may choose to unlock the phone and continue using their previous provider. Therefore, SIM locks are usually employed on cheaper (pay-as-you-go) handsets, while discounts on more expensive handsets require a subscription that provides guaranteed cash flow.
A practice known as box breaking is common in the UK and some other markets. This involves purchasing (usually) pay as you go handsets from retail stores, unlocking the phones, and then selling them (often abroad) for a higher price than the subsidised retail price. The SIM card that came with the subsidized handset is then either thrown away or sold or used elsewhere. This practice is entirely legal in the UK, and provides a de-facto limit to the extent to which networks are willing to subsidize pay as you go handsets. In recent times network operators have been insisting that new customers purchase substantial amounts of airtime at the same time as they buy a new handset, in order that the total price they pay comes close to the true value of the handset.
Unlocking via code
Some companies have begun to offer an e-mail unlocking service. This service requires that the individual who wishes to unlock their phone email their IMEI number, which is usually displayed by any terminal upon entering *#06#, to the company. The company will then process this IMEI number and email back an unlock code and instructions. Input the unlock code and the phone is unlocked. These email services are usually the most efficient as it is the same method most retail stores will offer. However there are several fake random number generators available, so you must be careful, there are only a few older Nokia handsets that can be done using this method. Newer handsets have random unlock codes which are generated at random with no order, the code is then stored in a database by the network or the manufacturer, thus these handsets can only be unlocked via code provided by the network or professional unlocking equipment physically connected to the handset. Some vendors also offer unlocking by physically mailing the phone to a technician.
Unlocking the iPhone during activation
The Apple iPhone is unique in that it sets the lock/unlock state during the initial activation step. During that step, the SIM lock is set or cleared based on information about the IMEI stored in Apple's database.
Spoofing SIM data
In 2004, a company BLADOX in the Czech Republic released a small device called a Turbo SIM which contained a small MCU capable of spoofing the network ID during SIM registration. This thin device sits between the SIM card and the phone, in the SIM slot. A small piece of plastic on the SIM is removed to make room for the MCU. The most popular of these devices, originally for the U.S Apple iPhone 3G, is typically called "Universal Sim" after a label printed on the card. A similar technique is used to "unlock" most Japanese phones as Japanese providers never provide unlock codes for their phones even after the contract is over.
Unlocking on-the-fly via software
To work around the iPhone's SIM lock system, a popular method used to unlock is to install a third-party software application on the iPhone which overrides the carrier lock temporarily.
Laws on SIM/network locking
Singapore is the only country that forbids outright SIM locking and contract/phone bundling.
The US and UK do not have any SIM locking laws, but American and British carriers usually offer unlocking codes voluntarily.
Many countries listed below have some form of SIM locking laws specifying the period of SIM locking and the cost of obtaining unlocking codes. However their effectiveness may be questioned when we look at the iPhone's worldwide distribution practices. The worldwide launch of the iPhone has definitively shattered numerous myths about whether some country has laws against SIM locking.
Australia
In Australia, carriers can choose whether to SIM/Network Lock handsets or not and usually tend to only SIM/Network lock prepaid handsets. There does not appear to be any regulation or law on SIM locking in Australia.
The lack of legislation in Australia is NOT in contradiction with the objectives of the Australian Competition and Consumer Commission (ACCC), the government body responsible for maintaining competition within the Australian consumer marketplace. Competition laws have to do with the number of mobile operators in the market (whether the government should auction additional mobile telephone licenses) and whether the mobile operators are price fixing or colluding. Consumer rights have to do with whether people are being mis-sold contracts, whether people have opportunities to get out of contracts, whether people are getting their defective handsets replaced.
Belgium
Currently there are 2 cases (VTB-VAB NV v. Total Belgium NV and Galatea BVBA v. Sanoma Magazines Belgium NV), in fro
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