Those with a new iPhone 4S who want to install Google's Voice app are out of luck for a while. Google was forced to pull the app after complaints about its stability arose. According to Google Voice Product Manager Vincent Paquet, there is a bug in the sign-in code that causes the app to crash immediately on opening. The bug only affects this most recent release and earlier versions of the app reportedly still work without error.
Google is fixing the error and will have a new version of the app available as soon as possible. As of the writing of this post, a Google search will pull up the information for the old version of the app. If you try to download this broken version via iTunes, you will receive an "The item you've requested is not currently available in the US store." error.
Google has not provided a time frame for when its revised app will reappear. Hopefully, it can get a fast track through the approval process and return to the App Store very soon.