Since upgrading to iOS 6 my phone has used large amount of data between 12 and 1 am, usually somewhere between 100-1000mb. What is my phone doing while I am sleeping to use up all of my data?
My money also goes to icloud backp; have a look at the time stamp if it fit and let us know. Other linked services activated: iTunes music, photo stream ?
True, but since the OP says they are sleeping at the time of the data usage, I figured the numbers were from their carrier usage itemize page... especially since they have such a specific time frame it occurs within.
Up to the minute usage is often just an estimate. At the end of the day, they likely do a true assessment and, if their estimates were low, they'd tack the difference on at that point.
As others have said, iCloud is also a possibility, but it's not supposed to back-up over cellular.