iPhone hidden feature: Prevent duplicate contacts

I just noticed a neat little feature on the iPhone I hadn’t seen elsewhere before:
If you manually dial a number, the iPhone will notice if it matches a number stored for one or more of your existing contacts and displays the name(s) at the top of the screen.
It also disables the “add to contacts” button, to prevent you ending up with duplicate contacts.

Not really groundbreaking, but indicative of the attention to deal found in every nook and cranny of Mobile OS X.

(Note: For some reason the video preview looks weird, but it plays fine once you start it..)