As others have said, it's universal. I live in Europe (Denmark), and it's nice to be able to send a picture to anyone with a cell phone. It's free to receive MMS here (I find it odd that you have to pay to receive one in the US). My little daughter had a friend over the other day, and it was nice to be able to send an MMS to the mother of the friend, so she could see what they were up to. No need to be pals on facebook, no need to have their email, skype account, or anything of the sort. The phone number is enough.
Obviously, if you want to send someone a good quality picture, MMS is not the best choice.