I have been trying to get FFMS working for some time now without sucess, I am on Vodafone UK and my settings are:
Access Point Name: Vodafone MMS
MMSC: http://mms.vodafone.co.uk?servlets/mms
Use Name: wap
Password: user
HTTP Proxy: 212.183.137.12
Port Number: 8799
Advanced Settings: 0.0.0.0 in all
Resize To: Medium
Network Mode: Polite, Havoc or Rude
None seems to work, some posts say that FAPN needs to be also used.
The settings in this reply have now worked for me, I unistalled FAPN and FFMS, reinstalled FFMS and set it up as Digicom mentioned, a useful post is http://talk.maemo.org/showthread.php?t=51890&page=37 with Havoc mode, and now everything works fine.