Except for "unlisted" numbers, land-line phone numbers are already openly published by Telcos in a way that links to owners' name and address. So the moment that a Facebook call is directed toward a "regular network" phone number, a link is established between the FB phone account (as well as the FB phone's user information, including location) and those phone-listing details of the person called (as well as how often calls are placed and when). It wouldn't take much to build a pretty fair linkage tree, based on merely that kind of info and just a little computer-based database correlation.
The really cool thing is that if you take such a FB-related call on your land-line phone, you immediately get linked into any such database related to the FB caller... including, potentially, all the data known about him (likes, dislikes, where he's been, what he does, etc) and all the phone-listing data about you (name, location, phone number, and any other data listings tied into any of those). Result: a kind of instant social network with no opt-in or opt-out capability for those being called.
Of course, Facebook would never, ever do anything of the sort to link such information. And, of course, neither would Bob ever sift FB's records to do it. Unless, as dib22
noted, they both already do...--
The American Republic will endure until the day Congress discovers that it can bribe the public with the public's money. A. de Tocqueville