Facebook shares a lot of information about you. Of course, you had to put the information up there to begin with, but with them always changing privacy policies and adding new "features," it's a good idea to keep on top of your shared information.
Maybe you're not aware of this, but there's a good chance you're friends can see your phone number on Facebook. In fact, check out your friend's numbers.
On your Facebook page click on the Accounts drop down on the top right hand side of the page. Click on Edit Friends.
Click on Phonebook
Tada! The phone numbers of your friends that have allowed Facebook display that information to their friends.
Concerned? Maybe you forgot that you gave Facebook that information and that you're sharing it with the whole world or at least your friends.
Here's how to hide it from everyone. Even your friends.
Navigate back to the Account drop down menu. Select Privacy Settings.
Click on Customize Settings.
Scroll down to Contact Information. There you'll see Mobile phone and Other phone. Click on the drop down and select Customize.
In the Customize Privacy pop up, click on the These People Drop Down. Select Only Me. You'll have to do this for Mobile and Other Phone.
Now your phone numbers are once again, secret. Unless you're in the phone book.