The trouble started after Apple blocked the Google Voice app for iPhone which then also involved the FCC and Eric Schmidt resigning from the Apple board of directors. However, it looks like both Apple and Google have worked over their differences since the Google Voice app is now officially available for the iPhone.
Google officially announced that the Google Voice app for iPhone and iPod Touch is available for download from the App store. The new app will allow you to make cheap international calls and provide free text messaging to US numbers. Google Voice for iPhone will also include push notifications and will involve making calls through Direct Access numbers.
Update: As pointed in the comment below, this app does not work on the iPod Touch yet. There are several comments on the app page which point this out too. I will figure out a way to get it running on the iPod Touch soon.