Google has realeased an App for the iPhone. Yes, Google voice has now come to the iPhone. google.com/voice/m.

The new Web service works on iPhones running the 3.0 operating system. It also works on on Palm's WebOS for user with the Palm Pre.
The new mobile-specific Web site for Google Voice is app-like in key ways. It's fast and it can use local storage, so it doesn't have to load in your entire Google Voice inbox every time you launch it. There's a dialer and a directory (tied in to your Google account) for looking people up. And, finally, you don't have to deal with Google Voice's dial-around service (where, to make a connection, the Google Voice service dials both the person you are calling as well as your phone). Through some telco trickery, Google Voice dials out from your phone, and displays your Voice account's phone number as the caller ID the phone of the person you're calling.