Try *777# Send to see which calling plan you have. Unless you topped up quite a few times you might be on one of the Sawasdee SIM plans. I think the government asked all operators to offer inexpensive 365 day validity plans as a form of consumer protection.

Validity varies by both calling plan and top-up amount, as indicated in the table I linked to in a previous post.

You can check your balance on line, and perform quite a few other activities, but you need to be able to receive a one-time password on your phone.

Go to http://www.12call.ais.co.th/en/Conte...eOne2Call.html

Choose "Online Services", enter your phone number 08xNNNXXXX, wait for the one-time password to be delivered to your phone as an SMS, then log-in. You can then check your balance and validity. You can originate SMSes as well, change promotions, enable international roaming, add data (GPRS/EDGE) plans, etc.