Make the iPhone say who's calling: "Now with the ability to create new ringtones in GarageBand, just record yourself saying the names of the people calling you most, then create ringtones with you saying that name, and add a ringtone following that in GarageBand. Share that as ringtone, and then assign the ringtones to the respective people on your iPhone. And voila, suddenly the iPhone will audibly announce the boss is calling or it's mommy!.
Mac OS X Hints - http://www.macosxhints.com