[lozf]

I agree with you, but sadly it's not that straightforward; It's entirely plausible (perhaps even likely) that your "facebook friends" have your number, and do something stupid^H^H^H^H^H^Hconvenient like give fb access to their address book (as is often requested, and I wouldn't be surprised if it happens by default with their mobile apps), Facebook are only one name match away from having your number and perhaps DoB and other personal info anyway.