The reason for this question is typically somebody is trying to use a SIM card other than that provided by the network operator who provided the phone.
Network operators sell their mobile phones at a much-reduced rate in order to entice customers into a contract of typically 12 or 18 months.
In practice what the operator is doing is adding the cost of the cell phone into the monthly contract charge for the service.
This is why they put in place restriction codes to ensure that the mobile phone cannot be used with another carrier while they recoup its initial cost.
This restriction can be lifted by entering an unlock code into the handset.
The type of code and unlocking process differs from handset to handset.
This code is called different things in different markets and even different hardware manufacturers.
The Code can be referred to as an: Unlock code, Network Unlock Code, Restriction Code or a Subsidy Code.
How do I get an Unlock Code?
To get the network unlocking code your first port of call should be your network operator.
If you are out of contract, although not obliged to, they will often give you the code.
Make sure you ask the company who supplied the phone and not the SIM card.
After the unlocking code has been entered you should be able to use the phone with any valid SIM supplied by any network service provider.
You can also buy an unlocking code from third-party providers and if you like to learn more on how unlocking codes are generated (including FREE codes) please visit this page here.
You are then free to choose a tariff or plan which best suits your phone usage from another network service provider even in another country.
A word of warning you also buy a new SIM from another operator you may find that your phone is now locked to that new network.
Also, the cell phone charges that will be applied for calls made on whatever network the new SIM uses may be much higher than what you could get if you were free to choose a SIM and service tariff, which best suits your phone usage, from another network service provider.
In other words, be very careful about what you are buying!
Anyway back to unlocking, once you have been given the Unlock Code by your operator or unlock service, the process differs from phone to phone. The following instructions are typical and should only be used for guidance.
Key in 00000000 or whatever the default password is for your phone. (8 x 0’S)
1. If you have changed your phone password, change your password back to the default 8 zeros (00000000).
2. Put your new SIM in the phone
3. When an Incorrect SIM error comes up, type *#9998*3323#.
4. White screen will appear with an exit option. Press the right softkeys.
5. This will reboot the phone and the normal service screens will appear.
6*. Type *0141# and then press the green call key. “Personalisation” or “Personalised” will appear.
7. Turn your phone off and put the original SIM back in.
8. Turn the phone on you will be immediately prompted to enter your password
9. Key in the default password as used above.
10. Your phone is now unlocked and free to use on any network.