No goof-up here: As planned, AT&T has successfully rolled out multimedia messaging for the iPhone today, and as far as we can tell, it’s not suffering any network outages or (worse than usual) service problems. That’s why it took so long.
If you want to use MMS, you’ll need to download the latest update from iTunes, install it to your phone, and restart your iPhone. Then, when you go into the messaging app, you’ll see the option to add a multimedia attachment (photo, etc.) to your message.