A friend just pointed out that the telephone numbers (home, cell) of its users are shown on Facebook. I do not know whether this is something new.
If you want to see your friends’ phone numbers: Go to the top right of your FB screen, click “Account,” then “Edit Friends”. Then go to the left side of your screen and click “Phonebook.”
Given the number of marketing trolls who try to get accepted as friends, this could be a problem.
If you want to control access to your phone numbers: Go to the top right of your FB screen, click “Privacy Settings,” then “Customize Settings” (near the bottom-middle of the table displayed). On the Customize Your Privacy Settings page, cursor down to “Contact Information,” where you’ll see buttons on the right that let you choose among levels of public disclosure.
In general, it is a good idea to review your FB privacy settings from time to time.