Hey again @Shaptoni
This isn't a feature that we offer at the moment, but I can see why it would be useful.
It would be difficult for us to give exact details of how your data is used though; we only have limited stats on specific usage through our own network, and if you're connected to a roaming partner this will be even harder for us to track.
There are quite a lot of different features that could cause your phone to connect to data overnight, for example app and software updates, as well as background app data usage.
Apple have a really useful help page on this that gives a breakdown of how to limit usage in the background, but the best way to make sure 100% that you won't see any data charges whilst abroad would be to turn off data roaming completely before you travel.
It's also worth resetting your data statistics prior to flying like @Christopher_G recommended originally, as this is going to be the best way to see the exact app or service that has used this data should you connect.
Peter
