I got it around noon today.
It said something along the line of In order for MMS to work you will have to insert your number and when you hit okay (only option) you were taken to Settings-Phone.
I haven't tried MMS, I just thought of it as a bug, maybe AT&T opened something today?
I am on 3.0 beta 5, and do have the carrier files updated. I don't know how but on iTunes I could right click and install them. Under Settings-General-About my Carrier says AT&T 5.0. I think I used an older version of iTunes when I reformatted my computer last week. I don't honestly know, but I'm not complaining.
I'll try MMS here when my phone charges up.
Update - Nope, MMS didn't work when I tried sending a picture to my Verizon buddy.