Originally Posted by
lianluo
....As I recall it, I requested it online and they would take some miles, but no copay (so yes, I suppose that wasn't complimentary, but it usually only cost me 10K miles). ...
Mileage upgrades on full fare economy Y/B fares then and now can be done with miles only. It is up to 20K or 30K miles now.
But mileage upgrades on discounted fares require more miles and co-pays. And in the past most discount fare were not eligible for mileage upgrades.
But since miles were required, it was not complimentary.