I was able to link my google voice phone number with the application sipdroid pretty easily and it allowed me to make outgoing calls without using my phones minutes as long as I had an internet connection (wifi or 3G). For the longest time I couldn't figure out why I wasn't able to receive calls through sipdroid.

The answer is in two parts:

1. Add an incoming routing in your pbxes.com account. Trunk should be your google voice email account and the rest of it should be default.
2. Now login to your google voice account and tell google voice to forward to google talk

I had some trouble running my processor preferences pane after upgrading my Leopard to a Snow Leopard install, so I'm putting up this quick tutorial on getting it to run. The preference pane runs in 32-bit mode (forcing the system preferences to restart) and doesn't show in the menu bar for me, but it works!

1. Install the latest developer tools