Originally Posted by
teCh0010
is it possible to call and get the "pay flat fee at check in" style of upgrade over the phone, or only paying the difference between your fare and the lost available first class fare?
Somewhere in between. When people here say "FCM", they generally mean they got an offer for FC that was lower than the fare difference. Normally this is offered as an upsell on the website (though as a DM I've never seen one). But sometimes when you call in and ask they'll give you a very good rate.
These rates are generally tailored to you specifically, so what you get offered may be better or worse than anyone else. Anecdotelly, those with lower/no status seem to get better FCM offers.