USB Flash drives as e-tickets

IO Data is pushing a new electronic ticketing system in Japan that uses those little keychain USB Flash drives instead of paper tickets for concerts and sporting events. The way it works is that when you buy a ticket online it automatically puts your ticketing information onto the drive, which you bring to the venue with you to gain admission. Sure, this would work, but there's no reason why you couldn't do just about the same thing with cellphones (and in fact, they already are).