Last night I went to bed, put my Ipad3 4G into airplane mode and left it in charge. I have a sim card for internet on the go that I have used with no problems for the past two weeks. This morning when I woke up I noticed that the cellular option in the settings menu was greyed out like when you have not inserted a sim card. I rebooted and everything was ok again. Has anybody noticed such a behaviour? Thanks guys!