Sprint Customer advised not to upgrade to iOS 6.1.1
By Larry Thacker Jr., 18 February, 2013
iOS and iPadOS
I read that some were having battery issues after upgrading and that the problem the upgrade was supposed to fix seemed to be affecting European customers, so I threw out a question to Sprint support about whether I should upgrade my 4S and was advised not to do so. You may want to check with your carrier before performing the upgrade to see if it will get you anything but trouble.