OK, its pretty simple. Install Sipdroid http://sipdroid.org/
Got to Sipgate and sign up http://www.sipgate.com/ you get 60 minutes free for outgoing or forwarding, initially forward to a cell or home # so you can set up your number in Google Voice.
Go to Google Voice and add your Sipgate # as a forwarding number in phones. After Google authorizes it you can remove the forward from Sipgate.
Go to settings on your Sipgate page, your info there goes in Sipdroid.
Open Sipdroid, click menu - settings and fill in the first 3 lines. Authorization username is your Sip ID, Password is your sip password and server or proxy is sipgate.com
Now you should see a green dot in your notification bar - you are connected.
Open Sipdroid, call your Google Voice number from a phone and your edge will ring.
Slide up to answer.
Sometimes the call is a little crackly, headphones help for sure.