Looks like the answer to this question may possibly be yes sometime soon. Several companies that provide inflight entertainment systems on flights are in discussions with iTunes and iPod to make it so that their services could be made available on flights.

One of the ideas being bandied about is charging frequent flyer miles in exchange for music - not a bad idea as so many frequent flyers have had the experience of their miles expiring before accumulating enough for a free flight. Engadget writes about the potential inflight options.