Don't get too frustrated....MMS is working for a lot of us VZW folks on MightyROM, as well as other custom rom's.
If it is not too much trouble to re-flash, here is exactly what I do (when flashing) and MMS works with no issues (and roms run flawless)...
Hard reset (clear storage) > flash stock vzw 6.5 (program phone, make sure phone sends/receives > run task29 (
http://forum.ppcgeeks.com/showthread.php?t=116571 ) post #9 .exe from ziggy > soon as task29 is done put into boot loader mode (vol down + end key + reset button) > start flashing MightyROM (soon as it gets past 1% I take out the battery) > right after 100% when you hear usb is disconnected, unplug from computer > wait a few seconds, put the battery back in and hold vol down + send + end to hard reset > provision verison > program phone with *228 and make sure phone sends/receives calls > install imnut's cab > soft reset > verify it works.
I know it's probably waaaay over kill, but I don't have any issues with this method.
EDIT: If it's never worked on MightyROM for you, or if you're having several issues, you may also consider re-downloading the rom.
Edit #2: After flashing stock and custom rom, I program the phone with *228 to make sure the phone works (added above)