I've done it. I'll admit it.

On a flight a couple of weeks ago, I turned my phone on while we were still in the air (we were in final descent). Full story is we were running 2.5 hours late due to a combination weather/mechanical delay, everyone was panicking about connections to last flights of the night and not believing the flight attendant when she said it was very likely many of the connections were delayed too. So I turned my phone on and went to the airline's app to give everyone around me updates about their flights - including gates, whether there were other flights that could get them home that night, etc. It also meant that my phone was already up and running so I could call the second we were off the runway to get rebooked as I had missed my connection and there was less than 30 minutes until the last flight that had any chance of getting me to my ultimate destination the next day.

Oh and it was all done in full view of the flight attendant so tattling probably wouldn't have done you any good.