I just reinserted my AT&T sim in the N9 and I got an SMS as well. Definitely not a "heavy: user. My average use is about 500-800MB/month, I'd be lucky if I used more than 1GB/month so I don't think they flag accounts based on usage. The conspiracy theorist in me however says that Nokia (MS) handed over the IMEI's of the N9's to AT&T but for what gain? They must begetting something in return. I will have to try this on the N8 as well since AT&T wasn't identifying it either.