AT&T will bring a new carrier settings for the iPhone. The carrier promised to roll out MMS support for both the iPhone 3G and 3GS today (Friday), September 25. According to Engadget, the update will be available “late morning” Pacific Time (which would be early afternoon Eastern).

What to do?
You need to download iTunes 9.0.1 to make the MMS update and be sure that your iPhone is using the 3.1 firmware.

UPDATE:

The MMS for the iPhone has arrived in the U.S. The update is now available via iTunes for most AT&T customers. Just install the update and reboot your phone.