This debate has been going on for ages and my good friend Joe Stump tweeted about it and asked my thoughts.
The FAA has drawn a lot of ire for steadfastly refusing to relax the ban on all electronic devices during takeoff and landing, a ban which, as Joe points out, seems hypocritical when pilots use iPads on the flightdeck as Electronic Flight Bags (EFBs.)
As a recovering airline employee and airplane nerd, I have a couple of ideas on why this weird rule remains in effect; while modern cellphone pose no danger to modern avionics, there are rare combinations of very old cellphone and very old (analog) avionics that can actually cause instrument deflection (specifically in ILS). Instead of creating lots of exceptions to the rule, the FAA probably thinks it's easier to enforce a blanket policy.
Secondly, and far more likely, is the desire to eliminate passenger distractions during takeoff and landing in case of an emergency. By forbidding the use of any and all devices at those points in the flight, they can at least try and keep the cabin alert. You'll notice the ban also extends to headphones, even if they're not plugged in, magazines, newspapers, eyeshades, and is also the reason why the windowshades are always up and the cabin lights are dimmed for takeoff and landing.
While it's definitely a first world problem, I can almost see why the FAA continues to do it. I just don't understand why they don't come out and just tell us the real reason. We suck at paying attention when we're on our blackberries "Hold on, hold onnnnnne seeeeeec, just gotta send......this.....ok, what did you say?"