I know that nobody knows for sure but what do you think? Apple obviously likes keeping their designs clean and a red or green blinking light would be too jarring. But what about a white light similar to the Macbook Pros light? It can be hidden behind the glass so that it's not seen (similar to the light sensor) and when you have a new message the white light will blink softly. Obviously there should be an option in settings to turn it on or off but I think this would be a HUGE hardware improvement to go along along with the new notification system expected to arrive in iOS5.