Upgrade for Android and Apple iPhone Vonage Mobile Facebook app
The Vonage Mobile application for Facebook is free from both the Android Market and the App Store. The software allows users to make free worldwide calls to other Facebook members who have downloaded the app. Calls can be made over both 3G and Wi-Fi connections. Besides heading over to the appropriate applications store, you can learn some more information by clicking on the source link.
source: Facebook (Vonage)