Facebook recently added free calling to their Facebook Messenger app for iOS users in the United States, however they will soon be rolling out the same feature for BlackBerry smartphones on their native Facebook Messenger app. This is very similar to BBM Voice in a way, but with your Facebook friends in the United States.
It is however limited in a way that you cannot make international voice calls, yet. Hopefully their voice calls for Facebook Messenger come to BlackBerry soon as they have stated, even though RIM is currently ahead in this category with BBM Voice as it is not limited to US only.
Source: BBC