You can do that with Facebook, too. In fact, Facebook does not know and has never known my phone number. Or rather, I'm sure it does know because my friends ha

You can do that with Facebook, too. In fact, Facebook does not know and has never known my phone number. Or rather, I'm sure it does know because my friends have me in their contact lists and shared that with Facebook, but it's not tied to my account in any UI way. I didn't have to opt out because I never even opted in.