I hope that it's a LED indicator that there is a notification. It's the one thing that I really miss from my Blackberrys, an LED telling me that there is a text/voicemail/email/phone call has arrived that I missed.
I'm always randomly turning on my iPhone and seeing that I've missed a text or phone call that I would have known about much sooner had there been a persistent indicator like pretty much every other smartphone has.
A subtle white glow like the one on a macbook/pro/imac when its sleeping to notify you of a message would be down right awesome and add to the sleek and professional feel of the phone.