I'm releasing a simple softphone as a vdr plugin. This plugin is available at http://club.telepolis.com/l.o/vdr/
From the README file:
This plugin is a very simple (read: not very featureful and hopefully with an high WAF ;-) softphone using the iax protocol (asterisk server). It uses the iaxclient library (http://iaxclient.sourceforge.net) to handle every details of the call, so the plugin is just an user interface. It needs a free (i.e it isn't used by something else, like a softdevice plugin), full-duplex sound card.
Enjoy