MMS works fine for me with the cab from this thread.

edit: I just realized there are a lot of cabs. I am using "imnuts sprint arcsoft mms 5.2.12.45 20100204" and it works perfectly for me, doing threaded MMS integrated into the stock WM client. I can even send and receive videos!

vin, after using your 8/20 for a day I immediately flashed back to 8/5 no-cookie via sd-card flash.
I was just having too many weird odd problems and lockups...it's just not nearly as rock-stable or fast as your previous build. weird graphical bugs as well.

I will be watching the thread to check for updates, I have my fingers crossed!