US used to have a 24 hour cancellation policy. I don't remember exactly when they (quietly) did away with it, but I believe it was shortly after the merger. It was a totally customer-unfriendly move to revoke the short window for "buyer's remorse," or allow for people to correct their mistakes, especially given how easy it is to make a mistake when booking on the internet. I can't tell you how many times I plug in certain cities or dates, and the website changes things on me for no reason!!!

Prior to the 24-hour cancellation policy, US used to allow you to put reservations on hold for 24 hours prior to ticketing. I actually liked the 24 hour cancellation policy better!