So it looks like T-Mobile is blocking wi-fi tether now. It was working perfect ever since I bought my S3, but today I turn on wifi tether and all is working then I get two text messages from T-mobile (see attached image). AS soon as I received the second message my tether stopped working. I am rooted running XquizIt v70 Rom, KT747 9-5 Kernel WiFi tether 3.2 beta 2. My computer I was tethering to is a MacBook Pro running Lion using google chrome browser.
This is just a heads up to you guys and if anyone knows a workaround let me know.