I finally got around to updating to the O2 OS. My pearl did the dreaded message delete and call lot delete 2 days ago. I had plenty of memory left and I've read the other possibility is an OS issue. So that was enough to prompt me to update to the new OS.
Point of all this is that my MMS is now working. As I've tested this a thousand ways now, I'm certain this is one key to getting the MMS to work with Cingular.
Incidentally, I'm using the
. Not the CINGULARPGPRS setting I was using initially.
For BES users, apparently the OS update does the trick.