Unlocking by IMEI is the fastest, easiest and safest method of unlocking your phone. The IMEI is a unique serial number that contains information regarding the type of phone, current software, when the phone was made etc.
It’s a number between 15 and 17 digits long (you will only need the first 15 numbers) which is the unique identifier of your phone. Type *#06# and press dial on your phone to retrieve your IMEI number.
Unlocking your phone via IMEI is the agreed method by all phone manufacturers. This method does not alter the original operating system of your phone, nor void the warranty.