Two of the most privacy-destroying forces joined together!
Yup, you'll be constantly prompted to enter your email address and password so it can find people to put into your contact book. At least, until it deems you have enough contacts
I'm sorry, but I don't trust Facebook with factual information about me
However, I bet there's going to be a market for this.
And, they'll constantly be updating your ringtones without telling you, and changing the way you dial. Maybe some days in reverse? Or, others in the order of the most popular numbers?