YouTube user diabeticHOWIE instructs you on how to enable MMS (Multimedia Messaging) for your iPhone 3G or 3GS. He claims that this may not work for the first generation iPhone. Using his step-by-step tutorial, you will be able to send multimedia messages to your friends and family.
1 - From the home screen of your iPhone, go into "Messaging."
2 - In the lower left-hand corner, click the camera icon
3 - Click "Choose Existing"
4 - Go into "Camera Roll"
5 - Choose one of your existing photos or videos
6 - Add text to accompany your photo or video as desired
7 - If you receive a multimedia message, you can save it, copy it, zoom in on it, etc.
You don't have to break into your iPhone in order to enable MMS, as all of the new iPhones are capable of it. However, AT&T did not make it widely known because they feared too many people sending MMS would crash their system.