Originally Posted by deathblade
To unlock your Galaxy S3 OR NOTE 2:
Just dial the following keys *#197328640#
Main 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 a minute then reboot your phone... enjoy!!!
*This is a PERMANENT UNLOCK, and does NOT trigger anything for warranty
Please note I have any copied and pasted from tuts I've found and things I've tried(with success) so this is in no way my finding I am merely passing it on
Sent from my Nexus 7 2013 using XDA Premium 4 mobile app
He said he already has the 4.3 MJB bootloader, and that his mmi codes aren't working because he is not on a touch wiz based rom.
The method you posted works only on the 4.1.1 modem and bootloader. It won't work with 4.1.1 modem and 4.3 bootloader. If you can't access mmi codes because you're on a custom rom it won't work...
To the OP try flashing something touch wiz based to see if that corrects your problem. I suggest something like S3Rx or the 4.3 official rom by loserskater, both of those are in the development section.
Sent from my SAMSUNG-SGH-I747 using xda app-developers app