I just got my Android on Sprint and it's the newest (no keyboard) HTC if that matters. SIPDroid APP which I tried to use but (like some of the other people that posted) the "New pbx linked to my Google Voice" box didn't appear at the bottom of the screen. That Blog and 'how to' I read was here:
Google Voice VoIP on Android just got a lot easier with PBXes peering | Kyle Hasegawa
My goal is to keep my GEO location private from any people, PI's, (or government agency) that may want to dig deep enough into cell records, etc. I can use Google Talk with the phone if this accomplished the same thing but I THINK that turning the Sprint Network off (with airplane mode) and talking over Wi-Fi is going to give me more of the privacy I'm seeking.
I have a phone.com account which is like many other PBX providers but I was reading where One Suite works well with some of this infrastructure but maybe they are all the same. You said that PBX.com is just a conduit for others to connect through. There seems to be some question whether to have a paid account with them or not.