Well all of you unlucky AT&T customers, update your carrier settings now! Plug your iPhone into your Mac/PC and open iTunes. Then, iTunes should notify you of a carrier update, install it.
This will not affect jailbreaks or unlocks or anything! So install away, then reboot.
No you will be caught up to 2005! 
Note: AT&T MMS will only work if you are on iPhone OS 3.1. If I can come up with a workaround for 3.0/3.0.1 users to use MMS, I’ll send it out.
Good luck!
I’m using the alternate APN. After U restarted my phone mms works fine.
Sweet! I’m glad it worked for you!