Apple has released iOS 6.1.1 but only for the iPhone 4S, at least for now. The update comes amid reports of cellular data issues preventing proper use of the device, originally released in 2011. Apple's release notes include mention of just specifically that:
This update fixes an issue that could impact cellular performance and reliability for iPhone 4S.
The update is available over-the-air (OTA) via Settings > General > Software update, or through iTunes via USB tether.
No word yet on a release of iOS 6.1.1 for other versions of the iPhone, or for the iPod touch or iPad and iPad mini. Apple did issue it in beta form recently, but likely expedited a limited version to fix the iPhone 4S-specific problems as quickly as possible. Whether that means the other versions are coming, or the next beta will be filliped to iOS 6.1.2 and proceed according to their original schedule is unknown.
If you've been experiencing cellular data problems with the iPhone 4S, once you've updated, let us know if they're really, truly fixed.