There is no need to install the valkyrie cab for MMS...here's all you have to do:
#1 made the registry edit:
HKLM\System\Inbox\ExternalAccounts and changing the name of the SMS key to SMS.htc
#2 updated the MMS server settings in HTC messaging to:
IP Address: blank
Port number: 80
Server address: http://mms.sprintpcs.com
Connect via: Sprint
Send limit: 1024 KB
WAP version: none
That's it! Can receive MMS just fine in HTC Messaging, but have to send through WM messaging