Understanding Mobile Phone Unlocking
This article will introduce you to the basics of mobile phone unlocking. It will give you an overview of common issues, help you distinguish between different types of phone locks, and help you choose the right unlocking solution for your mobile phone. It will also help you identify whether your phone has a problem that cannot be resolved by unlocking, or that renders it impossible to unlock.
What is unlocking?
Unlocking refers to removing the network restrictions on a phone so that the phone can be used with a SIM card from a different network. This term is often confused with the removal of other security or locking mechanisms, as described later in the document.
Throughout this document, the term unlocking will be used only to refer to the removal of a network lock (which locks the handset to SIM cards from a certain provider) or similar (e.g. subset lock, service provider lock, or corporate lock).Advantages of unlocking
- You can switch to a different network provider while keeping the same phone.
- When traveling abroad, you can use a local SIM card and avoid paying roaming fees to your home carrier.
- You can easily switch between SIM cards using the same phone.
- If you want to resell your handset, unlocking will significantly increase its resale value because it can be used on more networks.
- Increases the chance that your phone will be recycled. When recycled or donated phones reach their destination, many are thrown away because they cannot be used on local networks.
Identifying different types of network locks
Identifying the type of lock on your phone is an important step because it determines the procedure you will need to use to unlock it. The following are different types of locks that can be applied to phones.
Network lock (NCK)
Restricts the phone for use on one network only.
Android – Network locked
Android – Network locked
Windows Phone – Network locked
Network subset lock (NSCK)
Restricts the phone for use on a subset of a network only. Within the network, the phone is designated to work only with a subset of SIM cards.
Android – Subset locked
Service provider lock (SPCK)
Restricts the phone for use on a subset of a network only. Within the network, the phone is designated to work only with SIM cards sold by a specific service provider.
Corporate provider lock (CPCK)
Restricts the phone for use on a subset of a network only. Within the network, the phone is designated to work only with the subset of SIM cards provided by a corporation to its employees or customers.
There are two main procedures for unlocking phones: by code and by USB. Selecting the right service depends on several factors: which codes you need to remove the type of lock on your phone, whether your phone has 0 attempts left to enter the correct unlock code, the availability of services for your phone model, delivery time, and price.
Unlocking by code
Unlocking using an unlock code is usually the simplest procedure for the user. The phone’s IMEI (the identification number for all GSM phones) is used to look up in a database or calculate the unlock code (sometimes also referred to as a device lock code), which is entered to unlock the phone.
Note: unlocking by code may be impossible in the case that your phone is permanently blocked (there have been too many failed attempts to enter the unlock code). However, for some phone models it is possible to reset the counter and get more attempts, or to unlock the phone directly by USB without a code.
To unlock your phone using an unlock code, you will need to know your phone’s IMEI, manufacturer, and model number.
You can get your phone’s IMEI code by entering *#06#. The IMEI is a 15-digit number. It should appear like this:
or like this:
If it appears in the format below, ignore everything after the first 15 digits.
The phone’s IMEI is used to retrieve an unlock code. There are several different possible types of unlock codes: network unlock codes, factory unlock codes, and calculated unlock codes. The availability of any of these codes depends on the phone model and/or network provider.
Factory unlock code (manufacturer unlock code) Refers to an unlock code taken from a manufacturer database. The advantage is that these databases cover all models from the manufacturer. The disadvantage is that some network providers change the unlock code before selling the phone. In this case, the factory unlock code will not work. The factory code will also not work in the case that the phone is a replacement unit.
Network unlock code (carrier unlock code) Refers to an unlock code taken from a network provider database. If available for your network provider and phone model, has the advantage that it works even if the unlock code has been changed by the network provider. However, the network code will not work in the case that the phone is a replacement unit. These codes are available for a limited range of models and carriers only.
Calculated unlock code
Refers to an unlock code that is calculated from the phone’s IMEI, and in some cases, from the serial number and provider ID. A calculated code will be accurate even in cases where the network provider changed the unlock code or the phone is a replacement unit. However, these codes are available for a limited range of models and carriers only. These have the advantage of being (in most cases) available instantly.
Limit on number of attempts to unlock phone
Most phones will limit the number of times you can attempt to enter an unlock code. When the number of attempts is exceeded, the phone will freeze/block and stop accepting further unlock attempts (the phone will still be usable on the original network). In some cases, unfreezing/unblocking the phone is possible, but it is not always worth the cost.
|Brand||# of attempts||Reset?|
|Nokia||3||Reset is possible, but process is complicated.|
|BlackBerry||10||Can only be reset using a special device, usually costs more than a new phone.|
|Sony Ericsson||10||Can be reset at service center using special equipment.|
|Samsung||3||Can be reset using unfreeze code (MCK).|
|Huawei||10||Can be reset using reset key.|
Huawei – Reset key prompt
Unlocking by USB
Unlocking by USB is a slightly more complicated procedure than unlocking by code. However, the average user with no special technical training can manage either method.
Unlocking by USB can work by directly unlocking the phone and/or by reading the unlock code from the phone using software. When unlock codes are read from the phone, they are always accurate, even if they were changed by the carrier or the phone is a replacement unit. Direct unlocking by USB can also work even on phones that have 0 unlock attempts left.
There are several common ways to unlock the iPhone, but not all of these are risk-free. Using a risky method to unlock the phone can result in permanent damage that renders the phone unusable.
This is the official procedure for unlocking iPhones and the only method guaranteed to be safe. The user goes through the network service provider to have the phone unlocked. The unlocking has to be approved by both the network service provider and Apple. The network-granted unlock process is completed the next time the phone is connected to iTunes. The unlocked status will be detected automatically and the phone will be activated (unlocked).
Unlocking by USB
Unlocking by USB involves connecting the phone to a computer and replacing the firmware on the phone. The risk with this method is that after the iPhone is updated with modified firmware, iTunes may not be able to recognize the device, making it impossible to activate or restore the phone.
Unlocking by factory server manipulation
Unlocking by factory server manipulation involves having someone modify the Apple database so that permission is granted to unlock certain phones. However, once this is detected by Apple, the phone may be permanently cut off from service. The phone is left permanently unusable.
What unlocking won’t do
Distinguishing unlocking from other procedures
In some cases, there may be a problem with the mobile phone that cannot be resolved by unlocking, or that prevents the phone from being unlocked. There are also certain issues that people commonly believe will be resolved by unlocking, but actually they relate to a different procedure. These issues include:
- Phone is unable to detect SIM card.
- Phone cannot power on.
- No signal because of phone hardware failure.
To resolve hardware problems, contact your closest service center. Your local service locations are listed in the phone’s user’s manual.Network problems
- No signal because the phone hardware is incompatible with the frequency bands used by the network. This may happen because you are trying to use a phone model designed for GSM networks to connect to a CDMA network, or vice versa. See section: GSM & CDMA: frequency bands and your phone’s hardware, for more information about this problem.
- No signal because the SIM card has not been activated or paid for. (May appear as a “SIM not provisioned” message.)
- Network coverage on the desired network is not available in the user’s area.
The easiest way to troubleshoot network-related issues is to contact your service provider. You can find you service provider’s contact information in the booklet that comes with your SIM card, or saved on your SIM card.
Android – Inactive SIM card
Windows Phone – No service
Windows Phone – Emergency only
Phone is blacklisted
A phone may be blacklisted if: it is listed in a law enforcement agency database as being connected with illegal activity, an insurance claim has been filed for the phone, or payments were not made on the phone contract.
It is possible to determine whether your phone has been blacklisted by using a service that checks the IMEI against an international database.
It is very hard to recover a phone once it has been blacklisted. The original owner needs to contact the network provider, police, or appropriate authority that had the phone blacklisted. In many cases, this proves to be impossible. If anyone other than the original owner tries to remove the phone from the blacklist, the phone will be most likely confiscated. In most cases, blacklists are valid country-wide, meaning that the phone is blacklisted for one whole country but can be used outside that country.
SIM PIN & SIM PUK
There may be a lock on the SIM card to stop unauthorized users from using it. If SIM PIN security is enabled, you will be prompted for a 4-digit PIN code when powering on the phone with the SIM card in it. If an incorrect PIN is entered three times, the SIM card will ask you to enter the PUK. After 10 incorrect attempts to enter the PUK, the SIM card is rendered permanently unusable.
The PIN is provided with the SIM card when it is sold. If you need to find out the PUK code, contact your network service provider. Only the service provider (no other third party) is able to provide PUK codes.
Android – PIN code prompt
Android – PUK code prompt
Phone lock & screen security
There may be a lock on the phone that restricts the phone to be used only by the password holder. The user is required to enter a PIN code, password, or gesture to log in. Other users cannot access data on the phone and in most cases cannot place calls. Note: this is not the same as the SIM card PIN, as the security measure applies to the phone, not to the SIM card. In most cases, this type of lock can be removed by software update.
Android Screen Security – Pattern
Android Screen Security – PIN
Android Screen Security – Password
Windows Phone Lock – Password
A lock that restricts the phone so that it can be used only with one SIM card (the phone cannot be used with other SIM cards even from the same network). This type of lock can be removed, in most cases, by software update.
Software update (firmware flashing)
This refers to any replacement of the software on the mobile phone. The change can be an upgrade (replacement with new software), or downgrade (replacement with an older version of the software). In some cases, downgrading the software may enable the phone to be unlocked via root access or other means because of security vulnerabilities in earlier software versions. Software update can also refer to uploading either branded (specific to the network service provider, usually featuring the network provider’s brand on the home screen) or generic (original from the manufacturer) software.
This refers specifically to switching from branded to generic software. Debranding removes network-customized applications, branded startup/shutdown screens, and other network-specific settings. After debranding, the user can change internet (APN) and multimedia messaging (MMS) settings from those configured by the network. Note: some mobile phone models are designed for one network only and generic software from the manufacturer does not exist for these models.
This refers to attaining privileged control (“superuser access”) on Android devices, allowing the user to alter or replace system applications and settings, or run applications that require administrator-level permissions. For more information, see: Android rooting.
Jailbreaking is a process analogous to rooting, but refers to Apple devices. For more information, see: iOS jailbreaking.
GSM & CDMA: frequency bands and your phone’s hardware
There are two basic technologies used by mobile networks: CDMA (short for Code Division Multiple Access) and GSM (short for Global System for Mobiles). These represent two completely incompatible radio systems. Therefore, if your phone’s hardware was built to send and receive signals on a GSM network, you cannot start using it on a CDMA network, or vice versa, even if you unlock the phone. If you attempt to use a mobile phone on an incompatible network, the phone will simply not be able to connect. Unlocking the phone will only enable you to use it on networks compatible with the phone’s hardware.
Most mobile phone models are sold as either GSM or CDMA. GSM phones tend to have a removable SIM card, whereas on CDMA phones the equivalent hardware is part of the phone—but some CDMA models come with a CDMA “SIM.” GSM phones have a unique IMEI for identification, while CDMA phones have a unique ESN or MEID. There are also some “global” phone models that can be used on both GSM and CDMA networks. About 90% of the wireless carriers in the world use GSM-compatible technology, while about 10% use CDMA. Always make sure to check your phone manufacturer’s website for the technical specifications of your phone.
In addition to being designated for use on GSM or CDMA networks, phones may be compatible only with transmissions at certain frequencies. These tend to vary by geographic region. Some phones are “multi-band” or “quad-band,” meaning that they support transmission at multiple frequencies to allow roaming across regions with different transmission standards. More information about commonly used frequencies can be found at: Cellular frequencies and GSM frequency bands.
Before attempting to unlock your phone for use on a different network, make sure that the frequency bands compatible with your phone match the ones used by the network. Otherwise you will not be able to connect to the network, even after unlocking the phone.