That is incorrect. Google Voice is not a VoiP app and it will use your minutes. It will not use your texts, however. And the point is to have a separate, easily portable phone number, cheap international calls, free texts, and voicemail replacement.
Oh wow so say if I were to set up a google voice account, and down the road i was with a friend who had a droid phone but I left mine at home and needed to make a call, I could just log in to google voice and do it?