Facebook released an app update for iPhone, iPad (Mini), and iPod Touch devices today. This update brings free VoIP calling between Facebook users in the U.S. and Canada. You can call a Facebook friend from within the app. Here is the official description of all the new features included in this update:

• New button design makes it easy to like, comment and share posts in News feed.
  • Improved buttons to like, comment, and share posts
  • Share button to re-post stories from your News Feed now available in all languages
• Call friends for free right from Facebook (US and Canada) *Free calling uses your existing data plan.

Just remember that both parties need to have updated to the most recent version of the Facebook App in order to make or receive Facebook calls. To initiate a call, simply tap on the button in the upper right hand corner to see which friends are online. Tap on the friend you want to call and then tap on the info button in the top right hand corner. Then tap, Free Call. This will initiate a call. The option will be greyed out if your friend has not updated their app.