actually if you want to read the information Apple gave the FCC;
http://www.apple.com/hotnews/apple-answers-fcc-questions/
Contrary to published reports, Apple has not rejected the Google Voice application, and continues to study it. The application has not been approved because, as submitted for review, it appears to alter the iPhones distinctive user experience by replacing the iPhones core mobile telephone functionality and Apple user interface with its own user interface for telephone calls, text messaging and voicemail. Apple spent a lot of time and effort developing this distinct and innovative way to seamlessly deliver core functionality of the iPhone. For example, on an iPhone, the Phone icon that is always shown at the bottom of the Home Screen launches Apples mobile telephone application, providing access to Favorites, Recents, Contacts, a Keypad, and Visual Voicemail. The Google Voice application replaces Apples Visual Voicemail by routing calls through a separate Google Voice telephone number that stores any voicemail, preventing voicemail from being stored on the iPhone, i.e., disabling Apples Visual Voicemail. Similarly, SMS text messages are managed through the Google hubreplacing the iPhones text messaging feature. In addition, the iPhone users entire Contacts database is transferred to Googles servers, and we have yet to obtain any assurances from Google that this data will only be used in appropriate ways. These factors present several new issues and questions to us that we are still pondering at this time.