Associated Press | United Airlines said Thursday it has equipped all of its planes with Microsoft Corp.’s Zune digital audio service. The airline said passengers can listen to up to 21 different playlists programmed by Zune, from classic rock to classical music and soundtracks.

Airlines are busy adding diversions to keep passengers entertained and, in the case of wireless Internet access, make more money. Southwest and other carriers are experimenting with charges to see how much passengers will pay to surf the Web or read e-mail at 30,000 feet.