Sprint owners of the Samsung Galaxy S III will be pleased to know that a leaked version of Jelly Bean (L710SPRBLIF) is now available online for the phone. Even if you don't intend to try out this leaked ROM, the fact that it leaked and works well shows that the official one can't be too far off. Of course, several international versions of the phone already have their official Jelly Bean update, so it isn't surprising really.
If you don't mind trying out leaked ROMs check out the XDA thread below for more details, but as always be careful and follow the instructions carefully, because there is the possibility of bricking your phone.
Source: S3Forums via XDA