i had this on mine and my wife's omnia's after flashing and the verizon techs could not figure it out. so just clicking around i found this - go to the mms inbox - click menu - mms options - go to the profile tab - click on edit profile - make sure the mmsc is set to,
http://mms.vtext.com/servlets/mms - make sure te data connection is set to, Broadband Access(or whatever you have your connection named, there should be a drop down) - click done