Shtoom...

Sounds like a start on an open source applications platform for VoIP... from their site.

Shtoom is a open-source, cross-platform VoIP softphone, implemented in Python. As well as the basic phone, the package also includes a number of other applications -

shtoomphone - the end-user phone
doug - a framework for writing server-side voip applications.
There's a number of applications implemented using doug that ship with shtoom.
shtam - a simple answering machine/voicemail application
shmessage - an announcement server
shtoomcu - a simple conferencing server
Shtoom works on Windows, Linux/Unix and Mac OS X. The phone has a number of user interfaces - Qt/KDE, Gtk/GNOME, wxWidgets, Cocoa (OS X), Tk and a command line.

The phone has audio support on Linux using OSS or ALSA, on OS X using native CoreAudio, and on all other platforms using the PortAudio library. A native sound drivers for Windows has been implemented as part of Pythonwin, and needs to be hooked up.

Shtoom requires Python 2.3 or later, and Twisted 1.3 or later.