There's a difference between phone numbers and the Facebook directory. One is a user-owned identity which can migrate between carriers, the other a walled garden. With a phone number, I have an identity which can be linked to many services including Facebook. With a Facebook login, I am beholden to Facebook as my directory.
I'm not saying that this is relevant, because for the majority of users it isn't. I'm saying this for the hackers who just watched Facebook deny Voxer. If Facebook can capriciously decide who I can and can't talk to, that's not really what I would call an identity. What Facebook gives you is a slice of an identity, the slice it thinks you ought to have.
For many that is enough; for others it is an insult.
I'm not saying that this is relevant, because for the majority of users it isn't. I'm saying this for the hackers who just watched Facebook deny Voxer. If Facebook can capriciously decide who I can and can't talk to, that's not really what I would call an identity. What Facebook gives you is a slice of an identity, the slice it thinks you ought to have.
For many that is enough; for others it is an insult.