I J/S'd to BKK from SFO thru Narita and back on UAL with no problem at all. Everyone was very accomodating and even put me in first or business when it was available. I just showed up at the ticket counter in SFO and BKK and the gate in NRT. Make sure you show up plenty early though (2hr+). I only had to pay taxes coming back to the US and I think it was less than $30. Good luck!