You knew it was coming (Berman Post: Facebook Getting Voice Chat), and now it is here; in beta at least. Facebook's third party voice chat app has is now operational. I have not had a chance to try it yet, but the verdict from Mashable is;
"The app doesn’t work seamlessly, but it isn’t terribly difficult to set up either. After installing the Vivox Voice Facebook app, you must install a browser plug-in to integrate voice chat. Once you’ve done that, voice chat is activated. You can then invite friends that have the app to you voice chat. Inviting is done via a bit.ly link that Vivox sends via FbChat.
The bottom line is this: Vivox’s solution works, but it isn’t the heralded Facebook video chat that would be integrated directly in Facebook Chat. Until Facebook launches their own solution though, it’s a good alternative" (http://mashable.com/2009/10/05/facebook-voice-chat-beta).
Basically; it is ok for now, but hopefully Facebook will roll out their own better service in the not so distant future.