Note: these two answers are not mutually exclusive. You may stand by, but that does not guarantee you a seat on the next flight out. It's possible that there are literally no seats available on the flight for which you were not ticketed, but want to take. Or,they may choose not to make W inventory available. I have successfully stood by for an earlier flight when holding a W class ticket on Northwest. If you want to do this,your best bet is to call reservations and try to make the change. If they can confirm W space,you're good to go. If not, you can still try to stand by.