To unlock your Galaxy S3 OR NOTE 2:

Just dial the following keys *#197328640#

Main Menu >
[1] UMTS
[1] Debug Screen
[8] Phone Control
[6] Network Lock
Options [3]Perso SHA256 OFF
after choosing this option, wait about 30 seconds, then go back one step by pressing the Menu button then select Back, now you are in [6] Network Lock
choose [4] NW Lock NV Data INITIALLIZ
wait for a minute then reboot your phone

*This is a PERMANENT UNLOCK, and does NOT trigger anything for warranty