The updated carrier files that are floating around worked to enable the MMS options for me, but the messages would never send. I tried again a few minutes ago with the same result.
As a last attempt before waiting for the 25th to arrive, I checked my settings (again!) against a number of the various screen shots that are out there. Most of the ones that I've seen show the Username and Password fields populated. In one screen shot I found this morning, those fields were blank. I change my settings to match and I no longer receive the red exclamation mark.
My MMS messages are working.
