To find the IMEI number dial this code *#06#.

The unlock code is unique for every phone. You have to provide the IMEI number from your phone to get your unique unlock code.

When you have your unlock code, insert SIM card from another provider.

When the phone ask you for SIM network unlock PIN, enter this unlock code.

If your contract has ended, you can request the code from your provider. Another way is to buy an unlock code.