-------- CONFIRMED WORKING!! --------
well at least for right now its working.
I used a SIM from my old Nokia with a text plan from ATT. Make sure your SIM card can send and recieve mms on a different ATT phone first, follow the instructions above. The .ipcc file i used will be attached(---- FOR AT&T ONLY!!! ---), just change the .zip to .ipcc when you are ready to inject the carrier bundle with itunes. I had to manually add the MMSC and the proxy(for me it was MMSC:
http://mmsc.cingular.com Proxy: 66.209.11.32:80) make sure you dont touch the other setting under the MMS heading. Reboot and test. good luck feel free to PM me or what not if you have specific questions I will try to help the best i can!