"Well, they all sit on a Google Profile, and Contacts list. So I agree re user engagement, but architecturally (which is what I am really talking about) a centralized profile requiring login is common to all. This is not the right identity or contact list architecture. A distributed identity architecture leveraging devices people have in their pocket, is more likely to be trusted and functionally be way better than a centralized one (whether Facebook or Google). i think this exchange might be suffering from being typed instead of spoken. I sense I'm not being as clear as you need me to me. Sorry...." - Keith Teare