MMS Now Live on AT&T, New Carrier Update Available
AT&T’s carrier settings update that will enable MMS on iPhones running iPhone OS 3.0 and later is now live and available for download in iTunes. To get it, just plug the iPhone into iTunes, wait for it to check for updates, and select “Download and Update” when the prompt appears.
The prompt should look like this:
If you have any trouble, you may wish to consult the Apple Support Document.