With the ever increasing use of FADEC to control your engine(s), how can you ever be sure that the emi from your mobile phone will not cause the digital electronic controllers to malfunction and power down or fail the engine on your GA aircraft, or even on the heavier metal? I'm sure that it's safe on traditional carb/magneto engines, but modern stuff? There's no knowing what the risk is at present. Better safe than sorry, until they check it all out.