This is the rule published by American Airlines. Other carriers' rules may differ in details...

Devices with transmitting capabilities may only be used if the transmit capability is turned off and can be verified by a flight attendant (example: combination cell phone/PDA devices or laptop computers with wireless capabilities). During flight, never use cell phones (to make or receive calls), two-way pagers, radios, TV sets, remote controls (example: DVD, CD, game, or toy remote controls), a cordless computer mouse, commercial TV cameras, or Global Positioning Systems. Radio transmission using personal communications devices (example: walkie-talkies, two-way pagers, or wireless headphones) is prohibited, as it may interfere with the aircraft's communications and navigation systems.

http://www.aa.com/aa/pubcontent/en_U...ip_PersonalDev