From part of Patrick Smith's weekly column "Ask the Pilot" on www.salon.com

http://www.salon.com/tech/col/smith/...16/index1.html

"Why can't I use my cellphone during flight, and why are laptops also restricted? Even more annoying, we are asked to turn off devices as innocuous as portable CD players. Can these things really interfere with flight?

I'm asked about this frequently, but in researching the answer I'm confused by much of what I uncover. While I'm not an electronics expert, there have been several cases where devices (mainly cellular phones) have indeed interfered with the electronics aboard airliners. I can assure you the rules are not arbitrary or a scam to make you splurge on a pricey onboard satellite phone. One report cites a regional jet forced to return to the airport for an emergency landing after a fire warning sounded in the cockpit. Investigation revealed the alarm was triggered when a cellphone in the luggage compartment had begun to ring. I've also heard anecdotal evidence from pilots about times when cellphones have caused trouble.

Something of an easily digestible explanation can be read here. http://www.howstuffworks.com/question230.htm

There appears to be little evidence that laptop computers pose a similar threat, but the airlines are erring on the safe side. And a laptop, like any other carry-on, must be stowed during takeoff and landing to prevent it from becoming a 200-mile-per-hour projectile.

Remember that some devices, like Walkman or Discman players, are prohibited during takeoff and landing not necessarily because of interference, but so passengers are able to hear P.A. announcements and instructions in the event of trouble. In this spirit, maybe airlines should demand the removal of earplugs and wake up all the sleeping passengers, but it seems they've drawn the line at listening to music"