Oversea's Text

First off start saying SMS and not the word "text" when referring to this type of service or you might be meet with blank stares.

I for one don't use SMS message outside Thailand so not sure about cost of different plans.  Contact AIS (1 2 call) at 1175 and ask what your options are for SMS package.

While talking to them you might also ask about a GPRS package. I use this type of package for outside Thailand communications. Its a fixed number of hours for internet connectivity via your phone for a fix amount.  I pay 370 baht a month for 100 hours of connectivity. They have different package options from a few hours per month to unlimited for a set amount.  With a decent phone you can easily send and received emails via GPRS using your phone.  I can access all my internet email accounts very easily.

cheers,
straydog