That's what tmobile told me to do. They deducted the text charges from my bill and I replied STOP to the next few spam texts I got. I didn't have a real bad problem. Never gave out my mobile # or used it to register for anything, but still got the odd SMS spam once in a while. But haven't received one in a long time now.
I believe I've read you can have SMS disabled by the carrier, but it is all or nothing.