A few weeks back they mentioned that it was nearing the 3 million mark (which I assume references estimated sell through to consumers, while these new figures are shipment figures), and that it had already outsold the first Uncharted.
http://blog.us.playstation.com/2010/02/thank-you-for-a-great-2009/
Old figures:
New figures:
UNCHARTED 2: Among Thieves has also garnered more than 150 other industry awards, has over 1.5 million online users worldwide, and has surpassed 3.5 million copies sold worldwide – the fastest selling first-party title for PlayStation.
Of course, the blog post containing the older figures centers around 2009, so those may have been shipment figures as of the end of the year or something. I'm more inclinced to think they were estimated figures for sales directly to consumers.