It is inevitable for nearly all devices with heavy development that the occasional mistake is made and a device goes down. This is commonly referred to as bricking, and there are different kinds of bricks—soft and hard. While hard bricks are nearly impossible to fix without OEM support, soft bricks can usually be brought back. With the U.S. variants of the Galaxy S III, there’s already a soft bricking problem going around. Thankfully, there’s also a fix going around.
XDA Senior Moderator and Recognized Developer mskip has released a solution for users who accidentally soft bricked their devices trying to flash a GSM boot image. The devices are brand new, so there’s still a question of what works and what doesn’t, and flashing a GSM boot image is apparently one of those things that doesn’t work.
Each variant has their own files, but the process is identical. Users simply need to download their phone’s stock boot image and flash it via Odin. This should fix the issue and restore the phone to working status. It should be noted that these files are not factory tarballs wherein this won’t work if you need to restore to a stock, unrooted ROM. These fix only the GSM boot image brick issue. As stated, the process is identical but the files are different so be sure you pick up the file for your variant.