Google Voice for iOS

The official Google Voice App for the iPhone has been approved and now available on the App Store. Google Voice provides users with a U.S. phone number which they can use with their iOS device

You can download the app directly on your iPhone or iPod Touch through the Apple App Store or by using the link which follows:

Download
Price	Free
Requirements	iOS 3.0 or greater

With the native app, will continue to have access to all the major Google Voice features on your iPhone, like:

• cheap rates for international calls. 
• free text messaging to U.S. numbers. 
• Voicemail transcription. 
• Display your Google Voice number as caller ID when making calls. 

In addition to these benefits , the app provides some features that make the using Google Voice on your iPhone a much better experience.

• With push notifications, the app will alert you instantly when you receive a new voicemail or text message. 
• Most of your calls will be placed via Direct Access Numbers, making them connect just as quickly as regular phone calls.

source - Google