Requires iOS 4 or 5
Not Compatible with iOS 6.x
A system extension (NOT a standalone app) that seamlessly adds Google Voice messaging capability (send&receive) to iPhone's SMS module. SMS can be sent via Google Voice # in addition to carrier #; new incoming GV messages are notified and processed as system's SMS alongside with carrier SMS. Enjoy a true free unlimited SMS messaging experience with your favorite SMS app, including the built-in MobileSMS.
Now supports receiving Push notifications from Official GV App as native SMS messages!"
Now with an SBSettings GV Send toggle which controls whether system's SMS app sends SMS thru the built-in phone module (carrier) or GV messaging service.
Free trial only supports sending; for receiving a full license is required at $2.99
Go to product website | Support for detailed setup instructions
For Phone counterpart see Phone GV Extension on Cydia
This will not add any icon to your home screen; you can configure some options from Settings app.
See More Info for Screenshots