AT&T MMS in enabled in 3.0B2
I was comparing the differences between the 2.2.1 filesystem and 3.0 beta 2's and saw the carrier.plist had changed between the two. 3.0 added these these lines:
So that is why video and picture mms is enabled
I know there was already a thread saying someone had AT&T mms working, but I wanted to explain why.