Have you tried this method? I Found this in the MightyMike Rom Thread:
MMS CONFIRMED FOR VERIZON AND SPRINT!
*******THEY ARE ALL CASE SENSITIVE!!*******
MMS FIX FOR VERIZON, SPRINT AND US CELLULAR.
YOU DON'T HAVE TO DISABLE HTC MESSAGING
JUST GO TO MESSAGING TAB>ALL MESSAGES>MENU>SETTINGS>OPTIONS>MENU>MMS SERVER
THEN ENTER THIS DEPENDING ON YOUR CARRIER:
US Cellular
Server name: Your Choice
Ip Address: Blank
Port Number: 80
Server Address:
http://mmsc1.uscc.com/mmsc/MMS?X-USC-MDN=your number here
Connect Via: Data or USC Or whatever your data connection is
Send Limit: 1024 KB
Verizon
Server name: Your Choice
Ip Address: Blank
Port Number: 80
Server Address:
http://mms.vtext.com/servlets/mms?X-VZW-MDN=your number here
Connect Via: Data or #777 Or VZW or whatever your data connection is
Send Limit: 1024 KB
Sprint
To Get Your MSID Number Dial ##DATA#, then left soft key
Server name: Your Choice
IP Address: Blank
Port Number: 80
Server Address: http://mms.sprintpcs.com/servlets/MMS?X-SPRINT-MDN="YOUR MSID NUMBER"
Connect Via: Whatever you data connection is
Send Limit: 1024 KB
NO WAP FOR ANY OF THESE