By Amy E. Feldman

PHILADELPHIA (CBS) - What’s the point in having an airplane mode on a cell phone if you can’t use it on the airplane?

A traveler in Denver was kicked off a Southwest flight last month when he refused to turn off his cell phone. Is it really illegal to use a cell phone on a flight? The answer is yes.

Both the Federal Communication Commission & the FAA take a better safe than sorry approach to cell phone use. Both believe the radio frequency emitted by a cell phone could cause the airplane’s equipment systems to malfunction; that’s comforting.

But the law leaves it to individual airlines to determine when exactly before a flight you’re allowed to turn it off. Some airlines allow it until the flight is ready for takeoff, others as soon as the cabin door closes and some airlines are now preventing you from even putting the phone into airline mode, instead requiring you to actually turn it off.

You can face up to a $2500 penalty for violating the regulations and get kicked off the flight or even arrested if you get disorderly.

So, when the stewardess tells you to turn it off, you can go call someone who cares but not until you get off the flight.