I was able to successfully use both 3G data AND send/receive MMS with the following settings:
APN: simple
MMS:
MMS APC: simple
MMSC: h77p://smpl.mms.msg.eng.t-mobile.com/mms/wapeng (Replace sevens with "t"; new user controls...)
AUTH TYPE: None
All other fields are to be left blank.
As mentioned, these settings worked for me marvelously. ...For roughly ten minutes. Then the phone wouldn't wake up, I had to do a battery pull, and mms stopped working. When I go to check the mms settings in EM, it holds onto every value (including blank ones) save for the following:
MMS PORT: (blank)
AUTH TYPE: "None"
Whenever I select "Apply" to save settings, it always force resets those two values to the following:
MMS PORT: 80
AUTH TYPE: "PAP"
Hopefully this is all easy to understand. I've tried at length to search both xda and the world-wide-webz for an answer, but I'm coming up blank. I've always been able to figure this junk out for myself, but this is my first WP7 device, and I'm all kinds of 'tarded with it, haha.