You can privately chat with friends but in the past it has only been through typing, that is getting ready to change. Vivox is coming out with voice chat. Its not going to be through Facebook but as a third party app. Now when is it coming - sometime in the next few weeks. I guess its in a closed Beta testing now.

You can read more about it here:

Voice chat coming to Facebook

So I'm curious who will install it on their facebook and use it? I think they are hoping to take over the Skype business by coming onto facebook. Personally I don't chat on facebooks chat box - I'm one if I want to chat I'll pick up a phone so I don't really foresee me using it.