With the recent release of Facebook’s “Platform” for applications (see here for more info and links), my first thought, naturally, was… so what VoIP apps are in there?  Given that Facebook is being used as a email/IM/messaging platform by so many, the linkage into voice seems logical.  Oddly, when I went to Facebook’s “Application Directory” and searched (using the “Search Apps” box) on either “voip” or “voice” I wound up with no applications!  However, there clearly are some voice applications in there.  Through some browsing, I discovered these (note that the first links on each line will only work if you are logged into Facebook):

• WalkieTalkie – private voice chat for a Facebook group.  If everyone in the group installs it, they can all participate in a group “conference call”.
• Tag – from the same developer as WalkieTalkie, this is for one-to-one voice chat and leaving messages.
• Chatterbox – lets other users leave a voice message on your Facebook profile.
• VoicePlayer from Snapvine – let’s users leave voice comments on your Facebook profile
• Msg-Time – same idea… you can leave voice messages
• Free World Phone from Jaxtr – call-back service that calls users on their existing phones… also includes…