I must admit that this is a subject which has pre-occupied me for years.
Some years back major Australian airlines (following overseas practice) banned the use of mobile phones and other devices like laptops during take-off, climb and I think descent. But they could be used in cruise - whoops - not phones - but laptops and gameboys etc.
I commenced a study of this subject (at the time I was the Manager of the then Oz CAA Safety Promotion Unit). I could find no cases of electronic interference with flight or navigation systems directly attributable to the use of these devices.
I could find a fair bit of literature mind you. The incident reports were normally along the lines of - cockpit instrument deviation - can't find cause - ask cabin crew to see whether anyone in the cabin is using a device - yes sir - a kid in row 14f is using a gameboy - report it. I used to argue that they should be asking the cabin crew whther there are any blondes on board because then you could say this was the casue.
Now I don't know the answer - but if anybody does I would love to know the answer.