I should say that I haven't done this for over a year now, so things may have changed, but generally I would call the RTW desk for AA, BA general reservations, and Cathay's Marco Polo Club lines for the reservations; sometimes I get CX to do the BA reservations just because I was Diamond with them and that meant they would do rather more for me than for a non-status person. There's no charge (that's what the ticket collects).