[wackycat]

"There is a better way to handle this and that’s to use invitations sent by users. You can only connect to someone who invites you. There is zero spam and no need to validate email or phones, since you send your invitation to the email or phone number you personally know."

This does not seem like a robust solution. Also if you think of social networks as a network graph, then this seriously limits reach as you heavily rely on key folks who are a part of multiple networks of friends to invite those friends, etc which makes it really hard to scale. Any workaround to that problem, will inevitably introduce access for scammers.