Originally Posted by Mr. July
Another option on a same day r/t (especially if you don't have the ability to check in online) is to hit the kiosk at the airport when you arrive (i.e. PHX in your example) even if the departing flight isn't until that night.
I thought you couldn't check in using the airport kiosks any earlier than 4 hours prior to your flight? That is how it used to be before Online checkin, although I haven't tried it since, possibly the rules changed since then.