My apologies if I came off harsh. I just find that people are asking and using Google Voice and don't know the very basics of how it even works.. which is totally fine, everyone starts somewhere.. but there is a LOT of mis-information scattered around this board, and if you want to use it correctly, a trip to the actual google voice webpage is going to help so much to just get the basics. Because once again. There is NO free calling over wifi with Google Voice (unless you set up a sipdroid or similar account which I doubt given your question) So using the voice search when you are driving doesn't matter.. it doesn't matter how you get to your contact and make the call, because in the end, you still need a real verizon calling plan to make that call, regardless if you are using Google Voice.
I'm actually wondering how you got about not having a voice plan? As far as I knew it was mandatory on Verizon (data only plans I believe are only for the hearing impaired? Someone may correct me on this) Unless you just bought a droid and have never activated it.
The good news is Google bought out Gizmo5, a company that does VOIP, and will most likely be integrating the service into Google Voice, but that doesn't seem to be anytime soon.
So again, NO free wifi calling over google voice (without some big time sip setup)