There's not an "app" per se.<p>If you use Mobile Me and register your iphone with it you can track your iphone as well as make it play a noise for 2 minutes and show an alert.<p>As someone who recently had to replace an iPhone at full price (unwilling to sign up for another two years on AT&#38;T's horrible service in SF). I recommend looking into using this _before_ you lose/have stolen your iPhone.