Apple has practically banned any application that is powered by Google Voice technology from the Apple App Store which host mobile apps for iPhone and iPod Touch.
Apple rejected an application developed by Sean Kovacs which was based on Google Voice. He was given the reason that the application replicated functionalities already offered by the iPhone.
Google has already confirmed that Apple rejected their official Google Voice mobile application.
They have released versions for the Blackberry and Android platforms however.
Google Voice has been undergoing beta testing in the United States. The service allows the user to receive calls on a single number on multiple devices.