iMessage won't work after iOS 6 update?

I updated my iPhone 4 to the new iOS 6 update at around twelve today. Shortly after, I noticed my iMessage wouldn't work with anybody! I've tried resetting my network settings, and I also did a hard reset. Neither of those worked. When I turn iMessage on, it just says "waiting for activation" and then eventually tells me to try again, because the activation could not work. It does this for one of my friends with the iPhone 4s, but not for other iPhone 4 or 5 users I know. My FaceTime works, and I have a strong internet connection. Is there anything I can do to make my iMessage activate?