Does anybody know: Can you still purchase a Business Class upgrade at the gate counter for an AT flight if your flight is 1/2 AT and 1/2 SW? If you can, I'd assume you have to do it at the gate of the AT portion of the flight. Also, I see where SW is a participating airline up for the TSA "pre-screening" application and AT is not. So, again....what if your flight is 1/2 and 1/2? FYI - the flight I'm looking at is SW the 1st leg leaveing VA and AT the first leg leaving LV. Thanks!