About 5 years ago, a computer magazine aimed at mobile computer users hired a test lab to check out all sorts of consumer equipment aboard aircraft after its readers complained of the electronic restrictions. I do not remember the mag's name and sure wish I had saved the article, but the test results were really scary.
1) FM commercial radios (88-108 mHz in USA) will throw a spurious signal 21.7 mHz higher and lower than what the FM radio is tuned to. As you can see, this can easily put the spurious signal (from the set's Local Oscillator) right into the VOR band. A spur on 116.000 means the pax is listening to 94.3 (116 - 21.7 = 94.3). On a SuperBowl Sunday with folks wanting to hear the big game, the test lab found that each additional FM radio aboard would increase the spurious signal being transmitted.
2) CD audio players were the next biggest source of interference to the NAV systems.
3) I don't remember if the test lab checked out cell fones or not. But the concern over the newer wireless fones with WWW access is certainly justified.
If you have a radio tech friend who has a spectrum analyzer, ask to see it some day. Tune it just to the VHF VOR freq range and turn on a commercial FM radio and see how strong these signals can be! Of course, having a spectrum analyzer in the cockpit is overkill.
Check out
http://dspace.dial.pipex.com/town/pl...6/index_fr.htm for industry efforts to understand this issue. I understand there is even higher concern about this due to Fly By Wire cables running the length of the fuselage, etc.