Previously leaked as the "Click", HTC's Tattoo has replaceable face covers that you can also design yourself. It runs Android with HTC's beatifying Sense interface (as seen on the Hero), and has a 3.2MP camera, 3.5mm headphone-jack, and MicroSD storage.
HTC hasn't really said too much more, other than it plans for the Tattoo to reach Europe in October, and the rest of the world in the months after that.
Some guesses then: The screen looks about 2.8-inches, and it's possible the Tattoo could be cheap enough to cost nothing with a carrier subsidy/smartphone plan. Hopefully the Sense UI won't be as sluggish as it is on the Hero, but we won't hold our breath. More details when we got 'em. [HTC]