Cessnadriver, Cell phones may cause some problem for the towers or for FAA, but that is not the warning given by the FAA and airlines.
Honestly, I think they use safety as an argument because it shuts most rational folks up. You tell them its to avoid problems that don't directly affect them and your typical selfish American is going to go "So?".
And I pads and Game boys etc, don't affect cell towers.
You know the "shut everything off" attitude is simply a way to prevent folks from arguing with the flight attendant whether or not it is approved, etc. Also to keep people from being distracted/obstructed (such as by a laptop) during phases of flight where a rapid evacuation might be likely.
At least not legally. Mythbusters wanted to test this in flight and the local FSDO told them that if they did it off the ground, there would be issues.and I'll bet $100 you can't demonstrate that.