Today's dose of Facebook hysteria is currently replicating in the form of a viral wall posting:
EVERYONES PHONE NUMBER IS NOW ON FACEBOOK!! NO JOKE... Go to the top right of your screen, click Account then Edit Friends. Go to the left side of your screen and click Phonebook. Everyone's phone numbers are now being published. Please repost to let your friends know this is happening so they can remove their number....
Quite misleading. The phone numbers you see if you click "Phonebook" under "Edit Friends" in your "Account" menu are only those belonging to your Facebook friends who have selected to share that information via their privacy settings. The same is true of your own phone number and other personal details. What your friends see depends on your privacy settings. (NOTE: Your contacts' phone numbers will also populate your Phonebook if your mobile phone is synced with Facebook. If you don't wish this to be the case, change your sync settings.)
Nor is this a new feature. As has been the case for years, if members prefer not to share their phone number, address, or other personal contact information with friends or other Facebook users, they must choose their privacy settings accordingly, or delete those details from their profiles.
UPDATE: Mari Smith has compiled a helpful page for Facebook users on how to protect their Phonebook privacy.
UPDATE: New version of the rumor circulating as of mid-August 2011 refers specifically to mobile phone contacts:
ALL THE PHONE NUMBERS IN YOUR PHONE... INCLUDING YOURS are now on FACEBOOK! go to the top right of the screen, click on ACCOUNT, click on EDIT FRIENDS, left side of screen and click CONTACTS. you will see all phone numbers from your phone are published that you have stored in your mobile phone. TO REMOVE, go to RIGHT column, click on "this page." please repost this on your status, so your friends can remove their numbers and thus prevent abuse if they do not want them published.
Read more about it:
• Facebook: We're Not Giving Out Your Phone Number
• Facebook Faces Down Phone Number Rumors
• Alert: Facebook Phonebook Is Not a Security Threat
• Facebook Help: Profile and Contact Information Privacy