Just note that if you are intending to buy the card, buy when you are still at the arrival area, there was once where i left the arrival area and the next thing when i tried to go back and buy, the security tell me that i cannot enter the area anymore and hence i am unable to purchase the SIM card at the tourist price.
You mean cant go back to level 2 to buy sim card from the escalator where there is a security guard standing there ? I encountered at my three trips to bangkok last few months, just tell them you want to purchase sim card or your sim card got problem. Got two times, they told me to write my name etc on a piece of paper, maybe is to keep track who has used that escalator to go back to level 2 .