mms doesn't seem to work on wifi or 3g
here is how to fix the MMS for now, until I can come up with a better way
Download APN Manager by 81 Square from the Market
Unzip this file
ApnManager.zip
to your sdcard so the you have an ApnManager folder in the rooot of your sdcard that contains the xml file
go into APN Manager - Backup & Restore and click the restore button
Then reboot your phone
you should be able to send MMS