A cellular provider needs to be looking though. From browsing assorted Internet forums, it appears AT&T and T-Mobile US regularly spot those using Android phones on cheap, "non-smartphone" data plans and force those users up to higher tiers. N900 users, on the other hand, seem to slip by unnoticed. There aren't that many N900s in the United States, and the percentage of those sneaking around on non-smartphone plans is likely such a tiny fraction of a fraction that persuing it isn't worth the effort.

If the N9 isn't released in the US at all, then it would seem the odds are good neither AT&T nor T-Mobile will bother adding its IMEI range to their watch lists.