[bradleyjg]

Maybe I'm missing something, I've never used WhatsApp, but how do you get from it to mobile Google+ on steroids?

It's text messaging (including group text messaging) over the internet. In other words a very stripped down walled garden email system -- like we had on Prodigy in the mid 80s.

Once it got off college campuses, Facebook's killer app was discoverability. That guy you went to high school with? The girl you met at the party last weekend, and you only know her first name and who she came with? Your brother-in-law's brother who offhandedly mentioned that he had season tickets he wanted to split? All of them could be discovered on Facebook without having to tediously trace the chain.

I'm hard pressed to see how you can have a social network without discoverability, even leaving aside the text only nature of the thing. Pictures were were Facebook's zeroth killer app, without those it never would have taken off even at Harvard.