Motnot:

I agree with the earlier comments about missing the flight and showing up to catch a later flight standby, but you can also do it with an e-ticket. If it is the same day, the computer still recognizes the locator number and the ticket agent has always been nice enough to try and get me out on the next flight without any charges. A paper ticket would be handy though if you are trying to get a flight on another airline, but sometimes they won't take a cheap fare.