Hi, lhortt! Sorry it's taken so long for me to reply - I've been out of town. Check out this app, available for free in the Google Marketplace: 3CXPhone. It seems to play nice with VOIPo, and the calls are of good quality.

The problem, I've discovered, with SipDroid, is that it doesn't have the G.711 codec available, which VOIPo uses. Proxying through pbxes seems to solve that problem, but the 3CX has G.711 support, so it's a moot point. I really like the 3CX over SipDroid anyway - it seems to be a really well written app. They also make a windows version which works well with VOIPo too. Let me know how it works for ya!