I have an iPhone 6. I keep seeing weird data usage in the settings. For example, I facetimed with someone tonight. I made sure before I did that there was no cellular data usage under FaceTime in settings. I was connected to wifi the entire time. After I finish my call, I see 22.3mb of data used under FaceTime. How is this possible?! This happens for other apps too! They use data while I'm on wifi! And some apps still use data even though I have the slider turned off. I'm very careful with my data and now I have to check the settings regularly and I end up turning off my data because of all the weird usage. Any solutions?