I've used this option quite a bit when looking for SWU availability for flights I'm interested in using the AA website.. When I found one that worked and completed the itinerary online and put it on hold, I was then able to call the EXP desk and they could confirm the SWU and book the ticket for me. Unless there is an option I'm overlooking, it could now happen that I buy the ticket but when I call to confirm the SWU availability it doesn't actually exist. (And I've had a few occasions where they appear online but the agent can't see it or it no longer exists.)