Picture this: you're hanging out at a friend's house, and the familiar "doodle-dee!" of the iPhone's Tri-tone alert sound goes off. But four people simultaneously start reaching for their iPhones, because they're all using that sound for SMS/MMS alerts. Or how about this: you're on a bike ride and getting audio feedback on your pace from RunKeeper Pro. As you ride along, you hear the Tri-tone alert go off half a dozen times. Is it someone sending you an important text message, or is it just Twitter spamming you with @reply notifications?
If you're using Tri-tone for Messages alerts, there's no way to tell the difference unless you stop pedalling and check. Now imagine that your iPhone is more than ten feet away from you, or you're in a room where the ambient noise is above w
