Yeah, I have recieved multiple MMS messages and actually sent some out as well on TMO. I do not have the messaging plan, I just pay the 5 or 10 cents/message as I do not use that many.
I have the 8700C unlocked on Tmobile and receive/send MMS all the time. If you have a Tmobile family plan they will allow you to purchase unimited SMS/MMS for ALL accounts on the family plan for $9.99 (limited time offer).
Yeah, the launch devices from Cingular/RIM had MMS working, but then Cingular a week after disabled the MMS service books, so no more MMS on cingular, it works flawlessly on t-mobile like mas90 said...