Ok so MMS isn’t fully available on the iPhone yet, but at the weekend I downloaded a decent MMS application called MMS Photo Messaging.
If you really want you can go whole hog and send MMS but unfortunately it doesn’t link to your existing contract meaning you have to purchase credit seperately. I was never a big sender of MMS but I do like being able to receive the odd picture of snow covered roads or friends on holiday, and now I can!