I am annoyed by folks on cell phones, but the idea that they are some sort of threat to aviation is absurd. Some of the airlines are still using 60's-era avionics. Cell phones, through design or damage, can emit signals "out-of-band" and right into the aviation navigation and communication bands. The older avionics aren't able to filter it out.
Even more absurd is the idea that my computer, mp3 player, conventional radio receiver, etc. are some sort of threat.
All of those devices (especially the radio receiver) have an oscillator in them, generating a signal or clock at a specific or variable frequency. If the device is not properly shielded, it can radiate in the aircraft navigation/communication bands.
Since you are inside the metal tube, all of the RF is effectively pumped into the aircraft ground.
On the surface, it's generally not an issue. The flight isn't depending on radio navigation aids, and the communication stations are at the airport and so strong that they will overpower any interference.
However, in the air, it can be an issue. It's especially important on approach to the airport. En-route, the pilots have time to recognize and remedy the interference. I've been on a flight where there was an issue and the pilot asked everyone to turn off their electronic devices. My seatmate realized that his cellphone was still on. :-(
But in the end, it's not about controlling people. It's a liability issue. The FAA makes the aircraft operator responsible for prohibiting devices that may cause interference. They are only supposed to allow electronic devices that have been tested and certified as non-interfering.
Beyond that, the FCC prohibits operation of cell-phones in flight... even by private aircraft operators that can certify them as non-interfering. The reason for this is to prevent interference with adjacent cell phone base stations. Cellular system design reuses frequencies in non-adjacent cells, under the assumption that a phone on the ground can be heard in one cell, but not the other. An airborne phone casts a much bigger "shadow", and it's fast moving.
Some of the airlines are still using 60's-era avionics. Cell phones, through design or damage, can emit signals "out-of-band" and right into the aviation navigation and communication bands. Twaddle!
The only instrument I've ever seen suffer from interference of any sort is an ADF which is really just a fancy AM radio. Most of the ILS stuff is just above the FM band. Did you ever have any trouble with your FM radio reception in your car because a passenger decided to use his/her cell phone or listen to an mp3 player.
As for 60's era electronics, I doubt they move the old stacks to new airplanes. The percentage of airplanes in the US commercial fleet that were built before 1980 must be diminishingly low. Here's a picture of planes already out of service:
ML/NJ