I had a tough time with a new account, but here is how I fixed it...
Go to the gmail account, and load a profile picture. It will then appear to the left of the contacts list.
Click on the actual picture, and at the bottom of the pop-up, you will see "revert to Google Chat" Click that link, and then place a call, and you will get the message in the previous post. When completed, go back to Google Voice, refresh the screen, and you should see the Google Chat option at the bottom of the list.