Like using mobile phones at gas stations, this is an issue I've heard numerous justifications for over the years. One interesting one was the health effects of

Like using mobile phones at gas stations, this is an issue I've heard numerous justifications for over the years. One interesting one was the health effects of having 200-300 mobile phones ranging at full power inside a sealed metal tube in the sky. Not so much an issue for passengers, but flight crew on long haul flights subject to these signal levels for 8 or 9 hours several days a week! Obviously Airplane mode would solve this but telling everyone to switch off sounds a better way of enforcing this. Of course this assumes there are any adverse health effects from mobile phones at all, but that's a whole different can of worms. Another 'theory', I've since dismissed, relating to the requirement to switch off particularly at take off and landing, is because a plane load of 300 mobiles roaming between base stations at 400mph can cause the mobile operators a few headaches!