If you have flashed one of the Leaked Jelly Bean TouchWiz builds for the Galaxy S III then you probably noticed one big issue. It made the WiFi tether app unusable. Not to worry. Developer "TrevE" has developed a modified version of the WiFi Tether app that forces wireless tether on the Galaxy S III. It is pretty impressive that he was able to get this working without even having the device in hand. He relied on a team of testers who installed and reinstalled the app until they got it working. According to TrevE you will need to first uninstall any previous versions of the WiFi tether app before installing his version. Once installed you should not have to touch any of the settings. As long as you are running Touch Wiz Jelly Bean you will be good to go!
Grab the modified app here