There's a big notice on our wall about a Super Puma that lost its EFIS for a second or two on the North Sea when a passenger used a mobile phone.
Tune to an AM station, as used by ADF, on a cheap radio and switch on an even cheaper calculator nearby - you will find the radio is blanked out by white noise. In fact, the radiations from TVs and radios come within the VOR and ILS regions as well. Although cell phones are cleared for use near heart monitors (in hospitals), they do so at low power when inside the range of a cell. Once in an aircraft, and a long way away from a transmitter, they put the power up and then become dangerous - a couple of hundred phones searching for their cells can therefore create havoc.
Gameboys, video cameras and laptops are not immune either.
As for locking on to several cells at once - b*llocks. What happens when when you stand on a hill? The real problem here is the question of tracking, and is probably more to do with the FBI rather than the FCC, since the phone companies must keep the records for at least 6 months.
Modern phones transmit even when they are "switched off", particularly those multi PDAs - the only safe way is to remove the battery.
Phil