Log in to Gizmo5
Make note of your 1747... number
In the Google voice section enter your GV email address and password and save.
If you have an ATA: Change user settings to have your 1747.. number as the user id and enter your Gizmo password in the password part. The sip server should be the Gizmo5 sip server I think: proxy01.sipphone.com:5060
If you are having difficulty hearing audio when receiving calls you might want to use STUN server: stun01.sipphone.com:3478
Plug in your ATA
Log in to your GV account
In the settings --phone section enter your Gizmo5 1747... number you made note of above
Select Gizmo from the drop down box and save (This for incoming)
After verifying you will be able to answer using the ATA.
And you should be all set now to make outgoing calls and receive incoming too. If you are still having problems IM me and I'll give you more detailed instructions.