Originally Posted by
exerda
And it's possible he wasn't even actually using send/receive functionality, which is permitted for devices where it can be turned off (aka "airline mode" on cell phones, PDAs, etc.)
The FAA regulation requires that devices be power completely OFF, not just put in airplane mode, for taxi, takeoff, and landing. Once the aircraft is above 10,000 feet (usually only 1,000 feet or so on short-haul flights, whenever the captain sounds the first post-takeoff tone), then passengers can use approved electronic devices, including PDAs, Blackberries, and cell phones that are in airplane mode.
That said, I sometimes just put my cell phone and iPhone in airplane mode instead of turning them all the way off, and I've never had a problem during taxi/takeoff/landing.