The upcoming iPhone and iPod touch application, called GV mobile promises the remarkable functionality of Google Voice, directly in to your iPhone. It’s an perfect application that includes all the functionalities that you didn’t get from the default phone application, i.e. features like visual voicemail, a contact (and manual) dialer, and SMS support and more.
For more details watch the GV mobile demo video
http://www.youtube.com/watch?v=9IlvfEBJGx4 Be prepared to move to your Google Voice number as soon as GV Mobile is officially announced.
Sean Kovacs, the renowned iPhone developer, is the creator of GV mobiles.