Well they’ve done it in conjunction with HTC, so let’s not get carried away.
What Facebook have brought to the party is their own OS called “Home” which will run on Android devices and aims to remove the barrier between opening up the Facebook app and posting annoying updates to Facebook.

Instead, users of “Home” will see all their updates, friends and likes right there on the home screen. And also will be able to update and like from within any app. There’s not much more to it, so on the good side, it’s not complicated.

The device itself comes in red, white, black or blue and has a 4.3-inch screen and a 5MP camera.

More info: http://www.facebook.com/home