Q: iMessage stopped working suddenly

I just noticed today that I am unable to send or receive iMessages on my iPhone 4. I tested by using another iPhone (a 3GS) nearby to send and receive messages. SMS goes through, iMessage does not.

Changing the time zone settings and restarting the phone has not helped. Neither has changing DNS server to Google's (8.8.8.8). I do not have the time to restore the entire phone, and that solution seems like using a sledgehammer to me anyway.

When I disable then re-enable iMessages in my settings, it just shows the "Waiting for activation..." message forever. Also, attempting to sign in to Facetime (which I believe is related through my searching on these forums) with my Apple ID results in it saying it failed, and asks me to try again. One of the more useless error messages I have seen in my day, by the way.

So, basically, the other iPhone in my house, on the same wi-fi network, can send and receive iMessages. Mine however, cannot, and will not activate. Apple wants to charge me $29 for the pleasure of speaking with them, and that is not an option, since this is their software and the phone is not jailbroken.

Any ideas?

iPhone 4

At&t

USA

issue persists on wi-fi or 3G