It told me 90% today.  
I don't think a response of anykind is wise, or going to some website giving them "hits".

ignore

Received spam text messages from this number; we do not have a texting plan - these cost us money each time! As other posters mentioned, replying not only validates the number, it costs us another fee to send the text message.

Is there ANY way to opt-out or block this number? AT&T's forums and tech support is notoriously UNhelpful.

Got a text message saying they could eliminate my debt by 90% too!  There's no way I intend on replying, because then they would most likely just start physically calling!  I'm on the Do Not Call list, but I don't think that covers texting their telemarketing garbage.  Thankfully my incoming texts are on silent unless it's from someone I have programmed into my phone with a different ringer!  Guess they figure since they'll get in trouble by calling they'll just start texting you instead!  Annoying!