im going to hong kong next week and i will get an non immigrant o visa. can i then come back to thailand and get a 30 day free entry visa and then leave a week later for vietnam. stay in vietnam for a week and then return to thailand and use the 90 non immigrant o visa?

Yes, don't fill in the visa number on your arrival card. Ask the immigration officer nicely for the 30 day stamp explaining why and you should be fine

Obviously it's all down to the discretion of the officer, but others have done it with no problem

EDIT If the man insists that you must use the visa, get a re-entry permit before leaving for Vietnam, this will protect your 90 day stamp so you'll only lose a couple of weeks.

Edited September 10, 200718 yr by Crossy

thanks.