Another new feature that appears in the iPhone 3.0 software is MMS photo sending.  However this is not fully activated until ATT activates it on there end.  Here are screenshots of a picture being attached to a text message.  Just go into photos and select a picture, then click on the share icon.  This will bring up a list of different methods to share.  MMS is listed and when chosen it will take the picture and add it into a message.

Again, this is not fully activated until ATT enables it in their service.

-Screem