After rejecting Google Voice over the summer, Apple has approved an app for the competition. Ribbit's new iPhone app is now available for download in the App Store on iTunes. The app is free, but you'll need a Ribbit account to use the app.
Unlike Google Voice, Ribbit's service is not free. It will cost you $30 a month. Otherwise, the service offered is the same: call management and voice mail which can be transcribed and searched.
Ribbit's iPhone app directs users to the device's native phone and SMS applications. This is perhaps why it was approved while Google's was not. Apple contends that their reasoning for rejecting the Google Voice app was that it tried to replace functionality provided by native apps.