Originally Posted by
sfozrhfco
I have done it many times. You do have to do it at the airport though. Simply ask the gate agent if there are seats. If there are plenty of seats they will let you know and put you on the list. If it is full, they are usually pretty clear that there is no chance you will get on--or that if you pay the $25 you will jump ahead of others on standby. Probably not an issue on a Saturday to LAS unless there was a mechanical problem or heavy fog causing flights to get cancelled or severely delayed. Should be less foggy now that we are into September so probably not an issue.
You can pay the $25 to confirm a change by phone. If you want to standby for free, it has to be done at the airport. As
sfozrhfco said, they're pretty upfront about the likelihood of making the flight.