Just discussed this on IRC, appearently this was discussed at the summit.

To implement sending/receiving somewhat properly appearently we are going to need some kernelwork. (I'm still unclear exactly what's needed - I assume it's the different routing and stuff discussed on the wiki page.)

The workaround for sending would be a sharing plugin (and a free MMS-gateway service, I assume).
Receiving... Hopefully your carrier sends you an SMS with a weblink to get the MMS.

I still think its possible to implement MMS sending/receiving with the limitation of having to tear down the current connection and opening a new one to the MMSC. Which would somewhat limit the functionality as true push MMS as it wouldn't function when using the connection, but better than nothing

EDIT: The kernel issue is with establishing a network connection to the carriers MMSC.