With the iPhone locked with a passcode and text message previews disabled, you can still see an incoming text message while you are in the emergency call mode.
The iPhone should just show the generic "New Text Message" preview, but instead it will show the part of the message (or whole message if it's short enough), and sender information.
You can get the full details on this bug, and screenshots of the iPhone from Karl's blog. Now we must sit and wait for Apple to fix it. Hopefully this won't take as long as implementing copy/paste for the iPhone.
[via Ars Technica]