Phones can be used on flights. (from The Economist. Requires subscription)
On an average transatlantic flight, several phones are usually left switched on by accident, and the avionics systems on modern aircraft are hardened against radio interference. No, the use of phones on planes is banned because they disrupt mobile networks on the ground. An airliner with 500 phones on board, whizzing across a city, can befuddle a mobile network as the phones busily hop from one base-station to the next.