I cannot explain what happened to put your phone on Airplane mode but I can help you to get out of it.

Just press the Menu button, then go into "Settings", then select "Wireless $ network settings", then you just uncheck the "Airplaine Mode" checkbox.

Once you get on an airplaine, just turn it on so you can access local applications like your mp3 media player or games and many other apps but disabling all network communications, usually forbidden in flight.