I have a US AT&T S3 (SGH-I747) that had tethering unavailable when I bought it.
I already rooted it, installed a bunch of apps and customizations, and also recently updated it to JB.
I followed the instructions on a couple posts on xda-developers, and even got the tethering option to appear and *seem* to work, but when actually connecting to the hotspot from any other device, it simply doesn't let me surf.
The problem may be extremely simple or it may be more complex to isolate and resolve - but I need you to take the lead and get it to just work for me.
I may agree to even flashing a different ROM, as long as you assure that all my apps and settings will get safely restored.
I will let you watch the screen of the device via skype video, and just tell me in real time what to do.