I'm not ready to commit to a Google Voice account yet, but I really like the voice mail transcription feature.
Is there an app that can do this?
An app by itself isn't going to provide the solution you're looking for. Voicemail isn't a phone feature. If you're using the standard voicemail then it's Verizon's voicemail system. Unless they designed it with API's or some other method for apps to access voicemail (highly unlikely) then an app-only solution is out. You'd need a repalcement voicemail system, like GV (or any of the others).
Unless, maybe, the app dialed your voicemail and then checked and transcribed your messages. It would be a terribly kludgy solution though.
On your Google phone. With a GPS that knows where you are. And they have your credit card if you buy apps.