I thought I would add a couple of things.
First, I have the Family Unlimited Txt plan and MMS did not work for me at first.
Second, to get AT&T to take off the MMS opt-out, I told them that I had two phones, one for work and my iphone for while I was at home. I told her that I switched out the sim card from the iphone to the work phone while I was at work and switched it back while I was at home. I continued to tell her that the phone I use at work had the ability to send/recieve mms but it didn't work and I had a friend that did the same thing only his work. I told her that my friend had called AT&T and the CSR told him about the MMS opt-out thingy and he took it off for my friend.
after that long line of bull, she said,"There is no such thing but I will look at your account and see if I find anything..............long pause............okay, sir, I enabled MMS on your account, if you have any problems please call back."
I didn't want to tell the CSR that I was running the 3.0 GM on my iphone not being a dev and all. Not that she would have cared on inkling. Still, thats how I got it done.
I will repeat, she told me that the 3.0 update would include MMS and it would work on my iphone when the 3.0 update came out. I realize that she is a mindless CSR drone (no offense to mindless CSR drones) so take it with a grain of salt.
