What is aeroplane mode mode?

It just disables all the GSM fuctions so that your iPhone doesn't cause any interference with Airwaves and frequencies.

Airplane mode turns off all radios - cell phone, Wi-Fi and bluetooth.

It is dangerous if Airplane mode is not used when on an aircraft.

I think it should be mentioned the reason for Airplane mode.

When you are on a plane and they announce that all cell phones need to be turned of you can turn on Airplane mode. As stated above all phone functions are turned off, but you can still use the iPod function and listen to music.

Mark

To expand on this a little more - the instructions are to turn off all such devices during takeoff and landing until being instructed that it is safe to turn on such devices - with the requirement that airplane mode be enabled when it is safe to turn the device on.

Look in the :

[iPhone User's Guide|http://www.apple.com/support/manuals/iphone>

under Settings - Airplane Mode

Very good point, at some times “all” electronic devices needs to be turned off.