Two things: 1. Using a mobile phone isn't generally dangerous providing everything else on the plane works fine and nothing would be interfered with if it wasn

Two things: 1. Using a mobile phone isn't generally dangerous providing everything else on the plane works fine and nothing would be interfered with if it wasn't. 2. Cell handovers at 30,000ft with an air speed around 500mph are really, really hard. The reasons for turning your phone off during takeoff and landing are wide and varied, but the long and short of it is that it effectively counts as security theatre. Take off and landing are the two most dangerous bits of any flight. If anything goes wrong they do not want people tweeting "OMG IM GOING TO DIE!!!!", they want them focused on bracing for impact. That's not the only reason (or necessarily a major one) but you get the idea.