Years ago I was told by somebody with no particular credibility that the reason mobile phones were banned on aircraft had nothing to do with navigation systems at all. Rather (conspiracy theorists should get excited about here) that the speed of a jet aircraft in flight means that the number of, err, repeaters, thingies, mobile receiving stations, whatever, passed over by the aircraft meant that the phone company concerned (there weren't many around then
) couldn't track the call and therefore no bill was able to be sent.
Hey, don't shoot me, OK? I wouldn't have a clue!
(I have to say though that it's nice having at least one refuge from the LOUD mobile user........ "I'M AT THE AIRPORT AND I'LL BE THERE IN TEN MINUTES!"