Correct me if I'm wrong, but I think CO upgrades require one to call at a given time before departure. This is a big gripe for me because one is not always able to make that phone call at the "magic hour." It'd be nice if they allowed you to make the phone call anytime after booking, and the upgrades clear at the "magic hour." No certs, just one simple request (either by phone or electronically), unlimited upgrades, no certs or other nonsense, and automatic clearance and waitlisting. That would be the perfect upgrade plan. I don't think anyone quite has it right, but CO is very close. If they'd just combine that with UA's automatic clearance so you don't have to be calling at midnight...