Originally Posted by
ITravelWayTooMuch
E+ as well as a C and F upgrades are many times offered during online check in. Also, as a DM Preferred you can buy 500 mile upgrade certificates in books of 4 for $200 a book. You can request and if available confirm the upgrade up to 24 hours out and then buy the certificate book at the airport.
Yes, this is also true, but be warned that many many many UA ticket agents have no idea what you're talking about when you say this is a possibility to US preferred members. It often requires endless phone calls to supervisors and angry people behind you in line.