OK so I'll throw a little of what I know in here... I spent like 5 days playing with HTC MEssaging 1.8 trying to get MMS to work... Now VZW has the opposite problem that Sprint has... sort of... Sprint cannot SEND MMS. Verizon can send MMS, and even receive the message for a new MMS, but HTC messaging is unable to download the pic/vid/etc.
Here are the "correct" VZW server settings (doing this from memory until I get HTC messaging installed again...)
Server Name: SampleMMSC
IP: (blank)
Port: 80
Server Address:
http://mms.vtext.com/servlets/mms?X-VZW-MDN=1234567890 (replace with your 10 digit phone #)
Connection: Verizon Wireless (or Data)
WAP: None
Size Limit: 1024 (though this is not critical, as a simple reg edt can increase this to 5MB)
These settings worked on an old MightyROM Impact back in Dec/Jan/Feb for send AND receive. For some reason, these settings do not work to download the MMS attachment anymore. This leads me to believe that VZW changed something recently (which may also explain the other non-HTC MMS issues some ppl have been having)...
Hopefully this helps, and I'll post back if I find anything new!