Originally Posted by transpac

Sorry but none of this information (quoted) is correct or accurate. There is only one type of pre-paid SIM, there are many top-up and expiry options and many, many calling plan/messaging/GPRS options.

FWIW, with a One-2-Call SIM and if you have a GSM1900 phone and a signal here in the U.S.A. (T-Mobile, for example) you can check your One-2-Call balance, for free, by entering *121# SEND. You'll get a response back from AIS with the remaining balance and expiration date. I'm not sure if you had to have enabled international roaming for this to work though. It works for me, and calls ring through from Thailand (not that I answer them, I call back on my U.S. mobile) and SMSes come through as well. You can top up, and extend the expiration date, from the U.S.A. as well provided you have top-up PIN, which somebody could get for you in Thailand (they could buy a card and email you the PIN): *120*13 digit PIN# SEND. You may be able to enable international roaming remotely via email to [email protected] .