I was trying to decide between booking a cheaper ticket on a plane with only coach, PE, and D1 or a more expensive coach ticket on a plane with C+ so that I could pay for the base fare online then call in to upgrade to C+ and have it paid for by me RC Visa annual travel credit (which pays for seat upgrades but not base fare). I had some other questions so called in before booking the ticket and since the agent told me you can't call in and upgrade to C+ after purchasing online anymore for int'l flights that is 1 factor that tipped me towards buying the cheaper coach ticket). Then I found out I could not select my seats on the Alitalia codeshare I booked and was going to get assigned a crappy coach seat at check in so I canceled the ticket within the 24 hour window and bought a new ticket on a pure Delta flight with C+. As soon as I bought the ticket I was able to upgrade to C+ online and use the credit card I wanted to pay for it.