Last night we announced that the Samsung Galaxy S3 came along with a Locked bootloader! Nothing has changed with that. However we now have root thanks to some developers over at Rootzwiki! They have come up with a signed boot.img that includes root. The method is similar to the methods for other versions of the Galaxy S3. You will need to flash the modified boot.img in ODIN from there you will be able to push your Custom Recovery to the phone via ADB. The only downfall to this method that i can see is that the boot.img is 1.6GB! If you can manage to get it downloaded you should be good to go. Check out the source link for Download links and full instructions.
This is a good first step! Via DroidForums