Well - Google aren't stopping today, are they? Navigation gets released for AU/NZ users and now Google Voice for iPhone.
The official app is out and features push notification for new texts and voicemails, something that the previous Google Voice apps couldn't do without a third party hack.
Supposedly the app is very "barebones" - but appears slick and fast. Not many settings can be changed from the app itself - but surely this will change over time, for now - go and get it!
Unfortunately - this is just for the US at the moment.