Ok so if you have an iPhone 3G or iPhone 3GS, you need to update to OS 3.1 if you haven't already, then download a carrier file update through iTunes to activate MMS. From what I can tell it's working for me. I was able to send a pic to my mom. She tried sending me one but it didn't go through so she tried it through the email way and it didn't work either. I told her to do a battery pull on her phone (she doesn't have an iPhone).
reporting in that mms is up and running for me as well. had some test/fun conversations with fellow iPhone users and non-iPhone users and all has been working fine. as far as how much I'm going to actually use this productively... probably not much. but it adds great comfort knowing that we now have this feature in case I will need it if a situation arises (even though my previous phone of over 6 years has been able to do it).
I did actually use it productively just today. I sent my sister a picture of my first black eye I've ever had. I got elbowed in the eye while riding Space Mountain: Ghost Galaxy.
yes, embarrassing I know.. but it's my first black eye and after I got over the initial shock of having one, I came to be pretty excited and proud of it. hahaha.