When the purchase price of the mobile phone to the consumer is subsidized with revenue from subscriptions, operators must recoup this investment before a subscriber terminates service. In order to secure their investments, GSM network providers implements a software feature called SIM Lock on the handset to prevent usage outside their network. Such subsidies are worth more than several hundred US dollars and in that’s why carriers also charge an early termination fee; another form to recoup the subsidy investment.
Insert a SIM Card from a different carrier than your current SIM Card. When the handset power up is completed the handset will display a message like those below if it SIM locked:
- Enter Subsidy Code
- Enter Unlock Code
- Incorrect Sim Card
- Insert Correct Sim Card
- Invalid Smart Chip
- Phone Restricted
- Sim Network Unlock Code
- Sim Network Unlock Pin
- Special Code Required
- Wrong Sim Card
An Unlock Code is a numeric string. When entered into a locked handset it releases the SIM lock restriction and allows the handset to be used on other GSM carriers.
Unlocking your cell phone has multiple benefits: It increases the resell value and marketability of your phone by not restricting the purchaser to a specific carrier, it allows the handset to work worldwide and eliminates the possibility of roaming charges; by allowing you to switch to a local carrier in the local region.
SIM (i.e. Subscriber Identity Module) card is one of the key features of GSM. It is a detachable smart card containing the user’s subscription information and phone book. This allows the user to retain his or her information after switching handsets.
It is a software capability built into GSM phones by mobile phone manufacturers. Network providers use this to restrict the use of these phones to specific countries and network providers.
A Hard Lock is a permanent carrier lock. Your phone will become hard locked by attempting to enter an incorrect SIM unlock code more times than your phone allows, permanently locking the phone to the current carrier. Each phone has different limits regarding unsuccessful attempts before the device becomes hard locked. The usual amount for HTC, Motorola, Nokia, and Samsung is 5 attempts, usual amount for LG and Blackberry is 10 attempts. The messages below are examples of what a Hard Locked phone will display.
Code Error, Please Wait …
SIMLOCK block unlock reset KEY
SIM network subnet unlock PIN
You have tried 5 times, please wait for timeout …
Unlock Attempt: 10 of 10
Contact Service Provider
Number of Attempts Remaining: 0
Wait before Enter Special Code
Cannot Undo Restriction
This phone only accepts SIMs from specific networks, and has been blocked.
No, unlock codes are permanent and do not expire.
Yes, as soon as the phone has been unlocked with us, it will stay this way forever.
The IMEI (i.e. International Mobile Equipment Identity) number is used by a GSM network to identify devices attempting to connect to them and therefore can be used for stopping a stolen phone from accessing that network. It’s only used for identifying the device and has no permanent or semi-permanent relation to the subscriber. The IMEI number includes information on the origin, model, and serial number of the device.
IMEI = 14 digits + 1 Check Digit
IMEISV = 14 digits + 2 Digit Software Version Number
IMEI + SV = 14 digits + 1 Check Digit + 2 Digit Software Version Number
The format of the IMEI is AA-BBBBBB-CCCCCC-D, (15 Digits) although it may not always be displayed this way. The IMEISV drops the Luhn CD (i.e. Check Digit) in favour of an additional two digits for the SVN (i.e. Software Version Number), making the format AA-BBBBBB-CCCCCC-EE. The IMEI+SV incorporates both the check digit and the additional two digits for the Software Verison Number, making the format AA-BBBBBB-CCCCCC-D-EE.