Adhearsion recently released v0.8.1 and has big things planned for 2009:
jicksta.com/posts/adhearsion-2009
There is also a Getting Started Sandbox here:
adhearsion.com/getting_started
This allows people to start developing apps without first having to install Asterisk and wire it all together. I invite everyone to have a look at Adhearsion, an open source Ruby-based voice development framework.
Note: Full disclosure, I am now a part of the project.