Oh i'm sorry. The shop name is DTAC. Actually, all 3 telecom companies, AIS, DTAC & True have shops on the 1st floor of the airport. But I chose DTAC because it was closest to me, the shop personnel speaks good English and they offer the SIM card in both micro-sim and normal sim card formats, there is no need for any cutting services. The shop personnel will also help you insert the sim card and test it out in front of you.
I bought the micro-sim for 99baht and topped up another 500baht. Used the iPad everyday for 2wks in my wife's hometown in the northeast province and in BKK and there was no issues at all. Remember, there is no 3G so Internet can be a bit slow.
Now, I have a BKK micro-sim card sitting at home till my next BKK trip!