here's the detailed step by step that I was too lazy to write:
http://iiordanov.blogspot.com/2009/0...-gv-guava.html
in my case, it's sipgate + csipsimple. since sipgate stopped giving out free accounts recently, the alternative is using the ipkall alternative (which has some extra, annoying steps)
the alternative to that, is install sipdroid and use its wizard that does all the GV/pbxes setup for you (I think) and shouldn't require much in the way of manual intervention. if no one else does, I'll give it a try this weekend and report back how easy or not it is, and if it works any better than last time I tried.