Apple today has released iOS 6.1.1 for the iPhone 4S. This is a maintenance release intended to fix an issue plaguing 3G users in Europe. The update is available OTA (or via direct download) and can be accessed through Settings > Software Update. It is believed to fix an issue that could impact cellular performance and reliability for iPhone 4S.
The iOS 6.1.1 update for other iOS devices has yet to be released, although beta 1 has been seeded to developers.