I posted this earlier this evening on Lonely Planet. Nok Air has finally put in place a system to again permit use of foreign credit cards to pay online for flights. A new highlighted box appeared on its website yesterday. As I understand it the card, as relevant, needs to be registered with "verified by Visa" or "master card secure code" to use the system, I have just used my card that is so registered to book 2 tickets to Trang, have selected our seats and received an email confirmation.
The next poster said he tried tonight but it would not work. The requirement would appear to be to have the card registered as appropriate with the card provider. Mine has worked in that my credit card account has had the charge debited, I checked as I stuffed about using the secure system and had a couple of attempts and phone calls to the bank, the mess up wasn't actually my fault however.