The problem is with the ICloud. When you are logged into the iCloud, it puts a "Settings" option in the cellular data setting. This messes up some of the other options, meaning the cellular data toggle doesn't stick or is false for some apps. I know this because I have 3 iphones. One iphone, I never logged into the iCloud and NEVER had the problem. The second iphone, the iCloud was not turned on and the problem never happened and then the ICloud was turned on and within 1 day the problem showed up. The 3rd phone (all iPHone 4s) had iCloud turned on and is now eating up data all the time on IOS 7.1, even when on wifi. The solution is tough, you have to rebuild the phone as new but DO NOT put you apple ID and password in when you set up the phone and DO NOT restore your phone. If you restore, the settings will come back and the problem will come back. Yes, I know this is difficult, but it was the only solution I found that worked permanently. Once it it set up, do not EVER log into the iCloud or the problem will come back. Use your PC to back up your phone. Until Apple decides to fix this bug, that's the only solution I found that works. Most people will not want to do this, I know, but once you start going over your data plan and feeding AT&T money for free, you might change your mind. My 3rd phone that has the problem used 500 MB of data in the last 3 days since upgrading to 7.1.