We have heard several rumors previously that Samsung will likely push out the Jelly Bean update to the Galaxy S III fairly soon. Another new leaked build of Android 4.1.1 just popped up on the web. This time it's for the T-Mobile variant, which suggests these rumors are accurate. From the look of the leak, the one for the T-Mobile version (the SGH-T999) is virtually identical to the one for the i9300 (the international version). If you use basic deductive reasoning it would not be surprising to see that Jelly Bean will be coming to the States very soon. Why?
All the previous rumors seem to solidify the probability that the international version of the SGS3 will start getting its update on August 29th. If the T-Mobile version of Android 4.1.1 is working and appears to be the same as the international version, then it's logical to believe we might see the U.S. version at that time too (at least the T-Mobile version). Of course, there is still no word on the AT&T, Sprint, or Verizon versions. More than likely the Verizon version will be the latest, but perhaps we might get surprised. We should know in a few days.
Source: S3Forums via XDA