ATT can handle MMS . ALL other phones do this on their network. The problem is that so many people got on their network at once for the iphone that it would put a lot of strain on the network.
If you did this to verizon i am sure thier network would have problems also.
Also the one carrier thing I think was apples doing not att's since apple went to verizon first.
I think people arent looking at this objectively and are blaming att since they dont want to place any blame on apple.