Just found this, might be helpful to some people, not sure if it works for all carriers or not
Alltel hasn't forgotten the Samsung Galaxy S II, and Jelly Bean is available for download right now
Customers on Alltel using a Galaxy S II will want to check their messaging app this evening, as Jelly Ban has been made available. Users are receiving a text telling them the update is ready to download to their computer:
FREEALLTELMSG: Get the latest update for your Samsung Galaxy SII. Download OS Jelly Bean version 4.1.2 from your computer. Visit http://bit.ly/XHB4dp
Upon visiting the link, you're then warned that this is only able to be done via a computer (Windows only) using the Simple Upgrade Tool from Samsung. What you'll be downloading is the official SCH-R760 4.1.2 build, and the included package will walk you through getting it installed on your phone.
While we prefer OTA updates whenever possible, the jump from Gingerbread to Jelly Bean requires more than just an update to the system files. Manually flashing it from a computer is probably the best way to go here, though we wish it was a more generic process versus a Windows only executable file.
If you have no access to a compatible Windows computer (Microsoft Windows 7, Vista, or XP) you should visit the closest Alltel dealer and ask for assistance. For everyone else, get to downloading!
Download and Upgrade Tool