How is it possible that my iPhone is using data when on airplane mode? All our phones are using data during the night when we are asleep.  I thought that apps were only supposed to update on WIFI.  But my phone is always on airplane mode at night unless I forget, so last night I put in on airplane mode, took a screenshot as evidence, and sure enough, a tiny bit of data was used at 6:00am this morning before I got up.  How is that possible?
@Tyson's comment provides some insight based on your checking the data usage with your carrier, AT&amp;T.

The time that is posted by AT&amp;T is the time that they added the usage to your account, not necessarily the time that the usage was done.

As an experiment, if you can spare one of your iPhones that long, is to set it in Airplane mode for a day or two and see what AT&amp;T reports.  This thread on the AT&amp;T forum explains some of the fine print.