I'm assuming flight mode on a phone means you can have your phone on, on an airplane, but does that mode do? I'm assuming it's something to do with electrical signals.
In which case could you turn it to this in a hospital? What about when I'm at 'oliver', they ask you to turn your phone off as the signal messes with the elctrical equipment (we're using radio microphones and we have a tv in the props room with a camcorder recording the stage and sending it to that tv)
Also the bluetooth and wireless (if present) will be shut down.
So yep, you can put it on flight mode and it wouldn't interfere with anything, but you also wouldn't be able to do anything with the phone other than use stuff already installed, such as games music and videos.