I know someone that did the initial internal report to Apple about this years ago. This is exactly what it is. They use your contact data to create what are ess

I know someone that did the initial internal report to Apple about this years ago. This is exactly what it is. They use your contact data to create what are essentially graph nodes in a database, even if you've never signed up. Not sure how much of that has changed since then. But contact data is by far the most valuable mined from phones. Facebook is no exception.