For those of you with a “locked” Galaxy S3 GT-i9300, there’s now a free, open-source app you can use a rooted Galaxy S3 GT-i9300 to unlock your SIM so you can use it on any network.
Remember, you will need a rooted Galaxy S3 GT-i9300 and please DO NOT TRY THIS ON U.S./Canadian Galaxy S3 variants!
Download SIM Unlock here.