There is no easy way to find mobile numbers. According to this article, Facebook displays all phone numbers for all to see. However, FB has been openly listing mobile numbers all along. DUH, why are people so surprised? They've been pulling this crapola all along and hoping you'll buy into the idea that, "We're doing users a favor!" ... unfortunately, most people do, believe them. It's known as "subliminal advertising".
As was my experience with most of Facebook's "defaults", this guy figured it out, by accident. As for their "help" tutorials, they're not what I would call "user friendly", especially for the lay person who has no or little computer experience.
I think Facebook should let members begin with NO "defaults" at all and allow them to SET what THEY WANT, or DON'T WANT. So many people blindly click the "agree" box, and never bother to read the legal fine print. And, if you don't read all their legal mumbo jumbo, you won't know what their "defaults" are or how to control them ... and there are so many people there who either don't care, don't bother, or don't know how to change and manipulate the "defaults" to their FB accounts. So, why shouldn't Facebook make it convenient for themselves, and their advertisers - so both can make more money by putting more of your personal information out there, making accessibility to you, your likes, your favorites, as well as your buying habits - it's all for their benefit not yours. But sure, why not make you think it's "making it convenient" for you ... yeah right.
So go ahead, just keep on givin' ... all that personal information y'all think is so much fun! Thanks, but no thanks!