It will be a fashion statement. Though, I personally think it could be a handy little gadget if they simply make it compliment the phone rather than fail at duplicating functions. Display caller id, allow answering calls, function as a bluetooth speaker phone, display alerts so you dont have to pull your phone out of your pocket to find out that no, someone is not texting you, there is an update angry birds, control your music player, and heck, even display the current time.
I could see it as useful, but not exceptionally so. It should appeal to gadget folk. The real trick will be making it smart enough but simple.