the issue the FAA is concerned with is volume of untested wireless devices. currently they have no standard of testing devices so they are illegal for use.
also they would be the first to concede that 1 device may not bring down the aircraft but if all 218 people in the back are all activating thier own different versions of wireless devices
you begin to get excessive bleed-over, which again has not been tested.
additionally turning you devices off for takeoff and landing is more of a form to keep you paying attention to the FA's so if an emergency occurs you can hear, see and obey the commands and not burn to death ensnared in your own wiry ipod/laptop harness of death and killing all your tweeting friends around you.
additionally fun facts, old style Cingular cell phones and a few others would scramble the Com radios when they rang below 5000 feet if you were close to the cockpit,(you would get a heavy chattering buzz on the coms, I had one it would scramble mine) even Pilots are required to fully turn off the aircraft laptops and store them during ground movement, takeoff, and landing. as you probably already knew those pilots using the Iphone were breaking Federal regulations.
I do agree that FAA really needs to do some testing as most WIFI and electronics are safe to use the problem arises when you go from 1 device to 200+ My example I use when I'm questioned in the cockpit by visitors is screaming babies on a airplane, 1 screaming baby is annoying but we can all deal with it. 200+ screaming babies would probably cause the plane to return to field....
Yap go to "settings" top option: toggle flight mode on/off. Dunno if this is only available on 4G model, but I have it
Talking of which: I have by now 3 times seen pilots use iPhones + Speakers to listen to radio music on flight deck, and if the phone does not disturb the systems it is lying on, don't care for switching it off