You can (easily) do that on Facebook, too. It even lets you view your profile from other perspectives. And it's even easier than calling the phone company to ask for an unlisted number.

This uses the graph API to search through "lost my phone / need ur digitz" groups. Of course, human error is the best "in" for a hacker, and one of the greatest places to look for vulnerabilities is rare combinations of use cases. (People usually check privacy settings, but NOT for "groups"). Mobile apps are another great place to check for vulnerabilities, because "mobile" is a parameter that changes up the combination and introduces the possibility for (privacy, in the case of Facebook) vulnerabilities.