On my iphone 4s, there are these cellular data usages ranging from 1MB to 80 MB between 1 AM to 3 AM. This happens everyday. anybody knows what's going on and how to avoid it? During that time I am sleeping and the phone is connected to the WiFi.
Secondly I have noticed that when I lock my phone, it starts using cellular data instead of WiFi!!!
I have iOS 8.
Try checking your data usage history, as it seems like a known issue. A lot of people did complain but I can not find a solution to it.
Best Answer
It could be something like this secret (well, not so secret any more) program as detailed in the Wall Street Journal:
I've noticed the same thing myself, and I hear light planes flying over my greater NYC area home in the early morning several times a week. Because I'm a bit paranoid, I turn off my phone at night.