Apple released iOS 6.1.1 update to fix the bugs in the iOS 6.1 update. This update is for the iPhone 4S only.
iOS 6.1 was released at the end of January . iPhone 4S owners overwhelmingly voiced their frustration on the support forum to report that the update affected the handsets 3G signals and also caused their batteries to drain quickly.
iPhone 5 owners are also experiencing similar issues since downloading iOS 6.1 but Apple has not addressed this problem.
To download iOS 6.1.1 for the iPhone 4S Click Here