Actually, I was being stupid. I just realized how they do it. The FB app has access to the contacts of every person who has me in their contact list. So basical

Actually, I was being stupid. I just realized how they do it. The FB app has access to the contacts of every person who has me in their contact list. So basically without me ever giving them the info they know everyone I ever spoke to on the phone. It's a brave new world.