I get this message as well, I got it when I got a blackberry & then I went back to my Cingulair 3125. AT&T has been ZERO help. I've been told to close all other messenging systems, which I did - even deleted. I've been told to text, QUIT, STOP, UNSUBSCRIBE, ETC... which I did & then that just prompts another text. Last night the AT&T lady said that when I get my text bill, there should be a 1-800 number associated with these texts to call to resolve it, that it has nothing to do with them. I feel like it's a software glitch of THEIRS?? Why else would my phone be fine, until I activated a new SIM card. Either way, you'd better hope you have an unlimited text message plan.