Vodafone UK (Contract) now working! My settings as follows:

fMMS Config:

APN: Vodafone MMS
MMSC: http://mms.vodafone.co.uk/servlets/mms
Resize image: 300 (I'd like to know what the min/max settings are for this...any suggestions?)
Phone number: My number

Connections config:

Connection Name: Vodafone MMS
Connection Type: Packet Data

Access Point Name: wap.vodafone.co.uk
User name: wap
Password: user
Prompt password at every login: unchecked

Advanced Settings - Proxies

Use proxy: checked
HTTP proxy: 212.183.137.12
Port Number: 8799

Sent and received MMS successfully. Many thanks to frals for the effort to get this feature working on the n900. Great stuff!

:-)