As I was testing VoIP with the OBi100 I wanted to test using my smartphones as clients.
Obihai has apps for iOS and Android. These apps traverse the Internet back to your house and use the OBi100 to originate the call.
I installed the iOS app on my iPad and it worked perfectly the first time. Then I installed the Android app. I noticed that it was last updated in October 2011. Unfortunately it didn't work as smoothly. If you want to see the blow by blow read this. As noted it works sometimes but not very often.
There is discussion in that thread about using other SIP clients and I tried that briefly but that was really non-trivial to setup.
Since my goal was not really to network back to my house and use the OBi100 I went looking for just Google Voice clients.
I found GrooVe IP Lite. It did exactly what I wanted and worked the first time. It makes and receives Google Voice calls from your Android device. You have to enable Google Chat in your Google Voice account but that should be done already for the OBi100. The Lite version only works over Wi-Fi but that is fine for now. There's a good guide for installation and use here.
Why didn't Google just do this with their Google Voice app?