Apple has gone ahead and issued an update to address the cellular performance issues introduced in iOS 6.1 for iPhone 4S users. This does not affect the iPhone 4 or iPhone 5, and there is no update for those devices as a result.
This update fixes an issue that could impact cellular performance and reliability for iPhone 4S.
It’s likely that Apple thought it prudent to issue the most pressing fixes as soon as possible, and will roll out a remedy to the battery issues found on the iPhone 5 in iOS 6.1.2.
To apply the fix, head to your iPhone 4S Settings/General/Software update or download the IPSW for manual installation.