My understanding is that you can use any airline with Magical Express when flying in to Orlando, just make sure you have your yellow tags on your luggage if you want the ME folks to grab your bags. The quirk is when you are leaving, Southwest is now a participating airline so you can use RAC (Resort Airline Chieck in). When I spoke to the RAC folks in May they said that they used to be kinda bored, but now that SW has been added they are really busy. It is a very nice addition to be able to just take your bags to the lobby, check them in, and not have to worry about them (well, at least no more than you normally worry about your bags following you on the plane). I had flown when SW was not a participating airling and had to lug my bags on the bus, I was so excited when I found that they were now a participating airline!