Facebook was clever to do Facebook Home as they did. As Zuckerberg said in an interview, doing an entire phone would have meant they would have reached much much fewer people than they can with the Android approach.
Here are some related blog posts/articles related to Facebook Home (and the bigger picture battle between Apple, Google, Amazon, and Facebook)
I Like It, but I Don’t Like It Like It
The Facebook phone is not as dumb as I thought it was going to be.
By Farhad Manjoo