Facebook recently launched its Home and Messenger apps in the United States. If you don't want use your minutes, you can use VoIP (voice over IP) with Facebook Messenger.
If you already at your Chat Head, tap on "more info" and launch the messenger app.
The feature was available on the iOS app, previously.
The call will be placed over WiFi or using the data connection. If the recipient has Facebook Messenger installed on their device, they will receive a push notification that allows them to see who is calling them.
Since the app works with cellular data, you will want to turn off data if you have a limited data plan.