Southwest has a policy of no cell phone usage even in "Game" or "Flight" mode once the doors close.

http://www.southwest.com/travel_center/electronics.html

For a device like the Treo, this raises the paradox of "is it a phone or is it a PDA?" What if, say, you possess this device but aren't subscribing to any wireless services and use it purely as a PDA? Does that mean that it is still a cell phone and is still subject to cell usage policies?