So maybe you should listen when your air hostess tells you to turn off all portable electronic devices, instead of cleverly hiding your iPhone in your sleeve; you might just be responsible for the next aerial crisis!
Portable electronic devices are classified as intentional or non-intentional transmitters of electronic signals. The list according to Boeing includes cell phones, pagers (who uses pagers anymore anyways), musical devices, etc.
Passenger carried PED’s on commercial airplanes can cause an interference with airplane systems, and they will usually be blamed for complications regardless of the true source of the problem.
Boeing is very strict about enforcing its PED policy, as one of its air planes nearly crashed when a man’s cell phone caused the auto-pilot to shut off. Maybe it’s a reflection on how addicted we are to technology that we can’t even cooperate with the people working hard to ensure that we have a 'safe and enjoyable flight.'