Originally Posted by CPMaverick
I've booked through US Air before, they let me directly enter a MP number at time of booking. Flight credited right away.
Of course this was awhile back and their website may have changed for the worse with the merger.
I can confirm, I recently booked thru USAirways.com (lower fare than UA.bomb for same US metal flights) and they specifically say that you have to call in to get non-US FF# entered.
One of many things that still need to be fixed post-merger.