Google has update the Google Voice application to support the iPhone 5, the iPad Mini, and the new iPad. Google Voice users are able to make one phone number central for multiple smartphones regardless of carrier, SIM card, and cellular plan.
The update excludes support for older versions of iOS. The cut off is at iOS 4.3. You can use the app to access your Google Voice account from the iPhone, iPad, and iPod Touch.
You can also use Google Voice to send free text messages to phones in the United States and make international calls at low rates. You will also be able to receive transcriptions of your voicemails for free.