We've already seen US carrier Sprint roll out the KitKat update to the Galaxy S III, and it looks like US Cellular could soon be doing the same. If you head over to the US Cellular page for the Galaxy S III, the phone is mentioned as running “Android™ KitKat” out of the box – the carrier hasn't said anything about its plans to update the third-generation Galaxy S, but the changes in the phone's listing seems to suggest that the update could begin rolling out to users in the near future, though we'll have to wait for more details to get a concrete time frame.
It remains to be seen when other major carriers in the US plan to start updating the Galaxy S III to KitKat, though with even the Galaxy S4 and Galaxy Note II not completely updated, we're guessing it could take a while. Sadly, the international variant isn't slated to get KitKat at all, so custom ROMs might just have to be the salvation for its users, unless Samsung can get around the issues it is having porting KitKat to its best-selling handset.