That's not the reason. The FAA doesn't give a hang about how many cell towers the phone might grab. Its the radio frequency (RF) signal interference that is the potential problem,
There are a lot of wires carrying signals that are running along the length of the plane. These are not shielded, as shielding is heavy, or at least heavier than no shielding. Therefore, these wires can act like antennas and pick up RF interference.
Also, some RF can or could also be picked up by the actual antennas of navigation equipment.
Any or all of these potential RF interference points might be adversely affected by the presence of any RF signal. That's why not just cell phones, but many electronic devices are banned. You can't listen to a radio on board, either, because of the very low power local oscillators present in superhetrodyne receivers, which almost all modern receivers are. These oscillators generate RF signals just like a transmitter, even if they are very low power.
The real problem, of course, is the possible interference with the navigation, communications, and instrument landing systems. If any of these don't work as they should, the plane's operation could be adversely affected. The only sane course of action is to ban all use of the kinds of electronic equipment that might interfere with these systems. I'm actually surprised that laptop computers are allowed.
Dave Head
