They don't recognize it! I am using one of them. But when you contact with representative they some times ask you your IMEI and phone model. If you will them IMEI from smartphone (including n900) then they will add you $30 unlimited. IMPORTANT: by new rules (from Sep 06, 2009) any smartphones (even you didn't get it from att) have to have $30 unlimited dataplan even if you don't want to use any dataplan! I accidentally have got this plan in September. Fortunately than I had contract less than 30 days and I cancel it.... Later I reconnect for another one.