AT&T forcing smartphones (even unlocked ones) onto smartphone data plans? (updated)

We've been hearing a few scattered reports over the last week or so that AT&T customers are getting nastygrams for failing to have a smartphone-approved data plan associated with their account while using a smartphone. Of course, if you've bought a subsidized smartphone (using AT&T's definition, which is a little vague and off-kilter but generally involves a smartphone operating system and a QWERTY keyboard) from the carrier directly, this is totally par for the course -- you should expect such a warning. Thing is, one of the long-vaunted advantages of buying an unsubsidized, unlocked phone and bringing it to the network is that you've got plan freedom -- the carrier typically doesn't really know (or care) what kind of phone you're using, so you can sign up for a cheaper data plan designed for feature phones. Well, we've got tipsters telling us now that they're receiving these notices on their unlocked handsets, and that "as a courtesy, [they've] added the minimum Smartphone data plan" automatically. A courtesy, indeed.

It'd seem unusual (if it's even possible) for AT&T to maintain a comprehensive database of IMEIs that are outside its sphere of influence, so we're thinking that this could be as simple as a situation where the carrier's last known record of the user's phone was a subsidized smartphone, but regardless, this is a pretty big deal -- for many users it means paying $30 instead of $15 for unlimited data, all the while paying significantly more for the handset upfront (at a savings to AT&T, no less). We're going to follow up with AT&T to figure out what's what here, but in the meanwhile, watch out for that email and / or text message of doom, folks. Follow the break for the full text of AT&T's communique.

[Thanks to everyone who sent this in]

Update: AT&T tells us that this policy has been in place since last September; folks who haven't changed phones since then are still grandfathered. Unsurprisingly, the company says that users with unlocked phones are more likely to be heavy data users, and that "the unlimited data plan protects them from sticker-shock bills." In other words, this policy is here to stay, which means one very, very important reason for buying unsubsidized has been taken away.