I use ultramobile for the same purpose for $10 month (paid yearly), you do need to add a little to activate roaming, but if you don't make any calls it just sits there.
Depends on the source country, some countries (such as the United States) have reciprocal tax treaties with Thailand that prevent double-taxation, so Thailand cannot tax you.
We are unable to guarantee that our numbers will work with phone verification services, such as the kind businesses such as PayPal, eBay and Craigslist use, that allow you to create accounts with other services. We cannot guarantee that our numbers will work or have never been used for the same purpose prior to your purchase, and as such, if we know about the verification service and it has been abused in the past, we will block incoming calls from such services.
We will not issue a refund if you purchase a number with an intent to use such automated account authorization and verification services and it does not succeed, regardless of your legitimacy for using it.
has a $10/month plan (paid yearly) that gives you a real US phone number that can accept texts from any financial institution (as well as make/receive calls, but that's expensive) It can be activated in Thailand. I had my starter sim card shipped to Thailand from Amazon. I also use it when I go back to visit the US which makes it convenient for me.
If you should ever decide to marry in Thailand, or to register an existing marriage. I'm not sure when else they might be required, but doing it while still in the states is pretty easy, but if you're not there, it's very difficult, even if you travel back for vacation, as it can take a long time to do.
Get your birth certificate and marriage certificate (if married) authenticated *before* leaving the US, otherwise it will be a very difficult process, and Thailand requires authenticated documents: