When your cell phone is purchased through a local service provider such as at&t, the provider will put a sim card restriction on the phone to prevent you from using your phone with another carrier.
Their strategy is of course to keep you paying for their service.
However, If you want to switch service providers and have the ability to use other sim cards when you travel, you will need to remove the sim card lock from your phone. You can “unlock” your cell phone by simply entering the correct “unlock code” into your phone using the phones keypad and the code we provide you.
Each at&t unlock code is specifically matched to your phones imei (serial number) and also via the provider and country its locked to, as well as the mobile device model number.
After you purchase your at&t unlock code you will confirm and submit your cell phone information to the unlock server. Your code will be generated and automatically emailed back to you with simple to follow instructions. No Technical Skills Are Required