I usually do not have a problem standing by on an earlier flight with CO, AS, or NW. Unless you consider getting the "middle" seat a problem. I do it all the time. But I have been told that standing by on a later flight is not possible because if you are a no-show at the beginning of your itinerary...they cancel your entire trip. There have been times where I've been running down the concourse huffing and puffing and wheezing, and the gate agent tells me, "Too late, the plane left". They then schedule me on the next plane, 'cause I'm coughing up a storm and having an asthma attack.

This is on same day flights. Only once when I was at the PDX NW ticket counter, the family next to me exclaimed, "Oh, the tickets are for tomorrow!" It was a young mother with two children. The agent said there won't be a problem, plenty of room, and ticketed her with no change fee for that day's flight.

It has always been change fee charge for me plus the difference in ticket price at the time I changed the ticket. The whole scenario that magic111has stated...well, I don't want to be at the airport all day long. I'm not being snippish, just realistic. Any airline, the average ta will have to ask the supervisor. I just cancel my original flight on the phone, and apply the ticket to the new one down the road. Of course, I live three hours from the airport, and it's hard to find a knowledgable ta. Look for the older guy in his 50's. I'm serious. No one under 35 for me.

There's also change fee for different connection cities even on the same day as the original ticket. Change fee for any sort of change that requires issuing a new ticket.

Good Luck.

Linda