Facebook made alot of noise with their Facebook Home app and the new features which came with it, mainly the Chat Heads feature which came as an update to the Facebook Messenger App. What they did not say anything about was the new VoIP feature that they added in the update.
This means that you can call your Facebook friends on their cell phone, without having their phone number. This was initially only available for the people in Canada but now it seems its working fine all over the world. This feature though has been found not working in low powered devices, (Did not work on the Galaxy S running Android 2.3 and HTC C running ICS) which is surprising.
To check if you have this option in your device then open a chat window and click on the “i” on the top right corner, there you will find a tab written “Free Call”. If you can make a call then congrats this service is available in your country now!