The GV app doesn't work on the zoom, but really shouldn't be necessary...
Here you go:
1. Download Sipdroid from the market and install it.
2. On initially starting the app, there will be a button at the bottom that says set up a free pbxes account to link with google voice. Press it.
3. It will automatically fill in a pbxes account name with your gmail account name. Change this if you wish, just write down what you enter.
4. You'll see right below that, it filled in the name of the gmail account linked to your phone. Again, this is important, and where I messed up, because I had a different google voice account than the account linked to my phone. For the password, make sure you enter the password for the google voice account listed.
5.Enter a sipdroid password. This can be anything. Press Create.
Dial, from the sipdroid app by entering the number on the main screen and pressing enter.
In the main settings screen, press the SIP Account at the top, scroll down and make sure you check 3G and EDGE if you have a 3G plan.
8. That's it! Make sure you write down or remember your pbxes account name and sipdroid password in case you have to reinstall sipdroid.