I have a jailbroken 3.0.1 3GS and updated using the file and instructions posted in this forum. After I updated and restarted, the MMS features were available, but I would get the red exclamation after trying to send pictures. I called AT&T who told me they didn't see anything wrong with my plan and that I would need to call a special iPhone service number (800-MY-IPHONE). While waiting on hold, I tried resending a picture and it worked! I sent another picture to another person and it worked as well.