So I set up the google voice, and called my phone from my wife's to test it. And I get a busy signal after I don't answer.
Mine had the same problem when I first set it up. I deactivated the phone in Google Voice under Settings and then Reactivated it and it worked fine after that.
You have to have a certain number of minutes on your plan. With a family plan, you have to have at least 1400 minutes to get it. You can access it through the Verizon website. You can add 10 numbers per family plan that are unlimited, no matter who they are with. And Google Voice is not a Verizon number.