I have an iPhone 5c and have iOS 8.4.1 with the $30 plan (100 MB of data per month). I found that I was running out of data on my phone even with cellular off, and not having used data for anything, and was thinking
that one of my apps working in the background was to blame. So I went to the cellular data screen and found that I couldn't turn off cellular for any of my apps...they were greyed out! Is there any way that I can turn off the cellular data for my apps so that I don't waste my data?
Screen shots of my cellular data tab in the settings app: (I know it says 0 MB used this month but that was because I reset statistics by accident. Before, it said something like 94.5 MB.) (And sorry, they're in the wrong order :P)