Okay, I managed to figure out the Verizon info for MMS - I installed the CAB in the ExtRom, found the settings there (verizon version is 3.0.6 newer one I have is 3.0.16 - prolly no real difference).
In any case, I then uninstalled the Verizon one, which restored the version from the custom ROM I built *and* kept the connection settings in the registry.
In case anyone wants to enter them manually:
Server Name: Verizon Wireless
Gateway:
Port Number: 80
Server address:
http://mms.vtext.com/servlets/mms
Connect via: The Internet
WAP Version: WAP 2.0