AT&T tweaking iPhone upgrade eligibility in advance of new model?

Wanting to buy whatever iPhone goodness Steve Jobs unveils later on today, but currently languishing in the grip of an existing AT&T contract?  According to MacRumors, multiple customers of the carrier are finding that, when they log into and check their account status, they're all of a sudden eligible for an upgrade where previously they were not.  No official word from the carrier as yet, but one obvious explanation is that they're preparing for an influx of requests from existing iPhone owners wanting to switch to the new iPhone HD.

Of course, we've seen things like this happen before, and had AT&T tell us that the system isn't a clear-cut thing but "based on a variety of factors (length of contract, payment history, etc.) unique to each customer's account."  We'll be live-blogging the whole WWDC 2010 keynote, so if you want to know whether what Steve Jobs announces is actually worth another two years of your cellular loyalty, join us at at 10AM PT (1PM ET).