The real answer is you need to go to another country for 10 to 30 days to prove your not trying to live in Thailand; Everything becomes easy after that
I have a second cellphone I use as a wifi hotspot for my us phone. My tello and mint do wifi calling back to the USA for 0 extra. If I want to call local use line or for real call I need to add talk time to plan, as I only have $10 a month data on the AIS sim