Some users of AOKP have had issues with mms. The biggest mms issue has been receiving mms messages on a separate thread (picture messages received come in on their own thread rather than in the same thread with regular sms messages). That's annoying right?
After playing with this thing for weeks and updating the mms apk on the rom several times to no avail, I've finally fixed it.
First off we need to go back to the mms app that was in the rom in previous builds. It will be put back in for all future updates, but until I update the rom you can use this flashable zip.
http://chiwen.shabbypenguin.com/Android/MmsUpdate.zip
Download the zip, boot into recovery and flash it. You can wipe cache and dalvik if you feel like it
Now, if we don't do anything else, mms and sms messages will still be received on separate threads. We don't want that. Fortunately fixing it is simpler than i thought.
Open the messaging app. Go into settings, check the box for group messaging, then uncheck it. Voila, mms is now fixed. Enjoy.
Thanks to mike28 for testing and confirming.