Jajah - Reach Out and Touch a Facebook Friend
Jajah has just released their new feature for Android users (iOS version soon to follow) to be able to call online Facebook friends anywhere in the world, right out of their phone address books. The Jajah app has been available in the Android Market for some time but the Facebook calling feature is brand new. While you do have to set up an account to use, the person receiving the call does not. (The below YouTube video shows an iPhone demo, but it is working now in Android).