As far as game peripherals go, Namco's GunCon is legendary. It's a great, great light gun controller. It would be a shame if Namco somehow cheapened that controller's good name by making an iOS app.
Today, Namco launched a GunCon iOS app for the iPhone and the iPod Touch called iGunCon. The good news is that it's free, and because it's free, it's difficult to complain that much about it. Let's not fool ourselves, though, it's not a GunCon.
The app can be used with iOS title Time Crisis 2nd Strike, turning your iPhone or iPod Touch into a wireless controller. Ducking behind cover and shooting are both done by tapping the iPhone/iPod's screen.