Facebook's own smartphone running their own customized smartphone platform.
HTC would manufacture the devices and fb may add their own crap on top of android. nothing special
from what i understand, a lot of people are very proud to be addicted to facebook. look at how much time they spend on it. look at how many photos they share on it.
Well a lot of my friends(especially girls) are addicted to FB but when i point out the same to them .. they deny it