Prior to about two weeks ago I was using my N900 on AT&T with the $10 MediaNet plan. No issues for two years. Of course, I could only use GPRS/EDGE with the N900, but that was ok because I have good WiFi coverage both at home and at work. The N900 never showed up in my account. It was always "unknown device". I guess because AT&T didn't have it in their database. Two weeks ago I picked up an International Galaxy S2. It does show up in my account but so far they have not changed my plan. So now I'm curious how long have you been using your GS2 with AT&T. Anyway I'm thinking that if they haven't charged you for the SGS2 it seems unlikely that they will for an N9.