Well, I was playing around with this last night and finally got it working thanks to that guide... I do have a few observations since I tried all but 2 of the SIP applications available on the market (The other two didn't download...?)
I could not get anything to authenticate to SipSorcery, but I did get them all (except the first two I mention below) to at least log in to SipGate. I don't really see the point of SipSorcery.
Sipdroid and aSip (Which are almost identical) don't like FroYo, at least not the RC2 build that I'm using, I kept getting errors about authentication. aSip worked once for the incoming verification with GV, but then it couldn't connect after that. They both seemed to have something funky with the WiFi, I had to keep toggling it on and off because sometimes they would *almost* work...
3CXPhone seemed the most promising as it is one of only two that I found with Bluetooth support... 'cept it didn't work with BT... Or the Mute button! It would also... I'm not sure if it crashed (It didn't FC, just... Disappeared!) when I would answer the call and then hit 1 to connect. It actually answered and let me stay connected twice, out of about 10 tries.
Talkonaut only works with Jabber-enabled SIP clients.
Mission-Tel dialer FC'd on every screen, I couldn't even set it up.
Fring would lock up my entire pone for about 2 minutes whenever a call came in.
CSipSimple showed the most promise, it had the best options and best call quality... I could hear perfectly fine with no latency, but noone could hear me... It *is* an Alpha project though, and I think I may contact them to help with testing.
Linphone was one of two that wouldn't install, I don't remember what the other one is.
And does anyone know why "Better to beg forgiveness" comes up in a search for SIP???

Anyhoo, all of the apps shared these same limitations, which are pretty much deal-breakers for me:
1) None support BT answering
2) Two "support" BT but didn't work (My headset has been used with 4 different phones, and my sister has the exact same model and used it fine with 5 others)
3) The audio on all of them was *extremely* quiet, and without fail, none of them allowed you to get into the settings to adjust the volume while you were in a call
I couldn't reliable test call quality because I was using my roommates MetroPCS phone, and he has extremely poor reception in our apartment (We had to do all the testing out on the porch just so his phone would work).
So, to summarize, it appears that this software is still in its infancy and shows a lot of promise, but I'm not thrilled with any of them, or how difficult it was to find any good information on this subject.
I am, however, more then willing to help out any devs that want to tackle this issue head-on.
Until then, I'll deal with paying for incoming calls and wait for Google to integrate Gizmo5 with GV
