United is now offering mobile boarding passes for customers who have iPhones, Blackberrys and other web-enabled phones.

Passengers flying out of Chicago O'Hare and seven other U.S. airports can receive an e-mail with a barcode that stores their flight, seat assignment and gate information. That way passengers can scan the barcode at security and when boarding the plane.

American Airlines, Continental, Delta and Alaska Airlines also offer mobile boarding passes