Well, I have a 6700 with verizon, and no data plan, and I figured out that i can get MMS thru the standard mail system, but what would happen is, when it tries to connect to data service, if i'm in EVDO it will fail. so since i'm only using wifi for real data, i forced the phone into 1x mode, and i can send and receive MMS just fine. connecting data for MMS isn't charged even without a data plan. as long as you have pix/flix msgs enabled on your account. hope that helps
edit: just remember to disconnect from data service after you send, and or receive the message