After all kinds of speculation - it is now clear that the Mystery third party iPhone App is none other than YouTube.
That's right, YouTube is hitting the Apple TV today, an announcement that is totally overshadowed by a little surprise Apple packed into the press release: YouTube is the iPhone mystery app. Sure, it might not be GPS or anything useful like that, but Apple seems to be aware of our addiction and is happy to oblige. YouTube videos can be viewed through an Apple-built application on the phone, and will be encoded in H.264 by YouTube to improve video quality and battery life on mobile devices. They'll have 10,000 videos ready by June 29th, and should complete transcoding the collection by this fall. Videos can be viewed over WiFi or EDGE, we don't want to even imagine the painful load times of the latter.