Moreover, why should it only be explicitly social apps that access the phone address book to find my friends? Why shouldn’t a retailer’s app tell me that I have 8 friends using it, and let me share products with them rather than emailing them dumb, untracked URLs or even, quite probably, screenshots of my smartphone with the app open?
http://ben-evans.com/benedictevans/2014/2/21/three-phases-of-messaging