I certainly have had PC speakers that picked up interference from a GSM cellphone. Cell phones are wireless transmitters that can transmit in the 3 watt range.

I certainly have had PC speakers that picked up interference from a GSM cellphone. Cell phones are wireless transmitters that can transmit in the 3 watt range. A typical CB radio is 4 watts. The radio in the airplane is in the 2-25 watt range, and it's trying to communicate with a ground station that might be a fair distance away. I don't think the real concern was ever that cellphones would cause planes to fall out of the sky, however, there's real reason to be concerned that they could interrupt the pilot's ability to communicate with ATC, which I'm sure could get dangerous. There's probably no faster way to get everyone to shut their phones off than a "this is your Captain speaking; a cellphone on board is preventing me from talking to the ATC" however.