I had time to kill before departing BKK in late November, so decided to purchase SIM card there instead of in town like I normally do (they didn't have the free SIM cards at Immigration like I got last time).
150 Baht included 100 Baht worth of minutes, and I didn't run out for a week (well, I don't talk much, see my handle
).
Had to set my alarm in Hong Kong, and when I turned on my phone it showed that I had service.
And at both booths there were plenty of tourists receiving information on various plans, so there are plenty of options from both companies, though don't recall the names right now.