I am attempting to use google voice and this is what I have discovered:
Download the google voice app for your phone. In the settings of the app you can decide to use google voice for your calls or not. When you dial out and you have chosen google voice from the app, it will dial a google number to place the call (randomly assigned, not your newly chosen number.) You can add this number to friends and family, but it can and does change. Therefore you could inadvertently use your minutes if the dial out number has changed. In the settings of the google voice app you can choose to decide with each call. I would personally not use google voice to place calls until you have a month with a lot of minutes left that you could afford to waste some playing with this. When in one area the randomly assigned dial out number is fairly consistent.
Place your new google voice number in your friends and family. All your INcoming calls will be free, regardless of how they originate (landline, t-mobile, etc.) The people who can call you free should still use your regular cell number, such as your family. Other Verizon people will be charged minutes since the google voice number is not a verizon number.
An option to make all calls free would be to bookmark the googlevoice page in your browser and place all your calls from there. At this time, I have not found a way to place calls from within the app.
Finally, there is a ringback app for google voice called GV by Evan Charlton. It is no longer being developed or supported. What this app will do is place the call and then your phone will ring back and the caller ID will show your google voice number. Then your outgoing calls will be free assuming that your google voice number is in your friends and family list. I haven't yet found a ringback app that is more reliable than this one.
You can also have a google number and choose not to use it until the google voice app is developed a little further while still having some of the other features that comes with it.
addendum: I forget if it is online or in the app but to get the incoming calls free you have to choose the setting that makes incoming calls display your google voice number as caller ID (the number you have chosen.)