If you’re one of those people who wished you could unlock your carrier-locked Galaxy Note II yourself to accept other SIM cards from other networks, listen up. Owl74 from the XDA forums has found a way to do that without any of that messy rooting or whatnot, and by just going through the menu of the device. While the original unlock trick was done on an LTE version of the Galaxy Note II, users from the forum has had success with other, non-LTE variants, as well as some Galaxy S III models. Interested? Here’s what you have to do:
Just dial the following keys *#197328640#
ain Menu >  UMTS >  Debug Screen >  Phone Control >  Network Lock > Options 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  Network Lock then choose  NW Lock NV Data INITIALLIZ
Wait for about a minute and reboot your phone. That should be it. Insert another SIM from another carrier to test if it worked.
It goes without saying that if you do decide to fiddle with the settings on your device, you do it on your own risk. But this simple step is pretty easy to do, and anyone with a functioning pulse should be able to do it for their device.
Source: XDA Developers