They are free on scheduled flights anyway And the films on offer when we went to Kefalonia were cack! Even better - I bought another set of headphones at the airport with an adapter so 2 sets of headphones could be connected to my MP3 player...also included was a connector for airplane sockets!
How come .. you are able to listen to your MP3 player on an aircraft. I got a bollocking from a stewardess on a flight to Cyprus when I tried to listen to my CD player. As good as told me I could single-handedly crash the frigging plane!
RE: How come Depends on the airline I think. Usually they just request electrical items such as CD players, MP3's, laptops to be switched off on take off/landing (which was the case this last time), though last year to Croatia they said for the duration of the flight.