You can text through GV for free but you can't call for free. You are still charged minutes. If you have Friends and Family, you can designate your GV number as one of your friends and all your calls will not add to your minutes. But, you still need a calling plan with F&F.
I do not have a text plan through Verizon. In fact, I have blocked all text messages through my Verizon #. I text all the time, back and forth, using GV.