The new app will go live later today at http://m.google.com/voice.
According to TechCrunch, "The new Google Voice mobile site shows your inbox with transcribed calls, which you can play from the browser. You can also send SMS messages or dial from the browser. The application ends up making a local call through your cell phone to Google Voice, which then routes your call through its own lines. When someone gets the call, they see your Google Voice number instead of your AT&T number. And when you get a voicemail, a notification even pops up on your iPhone with the transcribed message (through SMS)"
Although you are not able to access your iPhone contact list, you will be able to save a Google Voice contact list for use with the service.
A Google spokeswoman said the company had not received any updates from Apple regarding offering a native app version of Google Voice on the iPhone.
If you have a jailbroken iPhone you may want to check out GV Mobile +, an enhanced version of the Google Voice application that Apple removed from the App Store.