Just thought I would let anyone else on Orange UK know how I got MMS working.
Firstly I have a 2G iphone (8Gb) running the 3.0 (7A341) software which I unlocked and jailbreaked with Redsn0w!
I downloaded and installed mms2g via Cydia if you're unable to find it in Cydia just use the search option and type in "activate" and it'll show itself beneath in the results called "ActivateMMS2G"
Once installed I rebooted then went to the "http://help.benm.at/help.php" site via the iPhone safari browser. Go to the second Mobileconfigs link the one which lets you create a custom Mobileconfig, and enter these settings:
Mobile Internet
Apn: orangemms
Username: Orange
Password: Multimedia
Visual Voicemail
Apn: orangemms
Username: Orange
Password: Multimedia
Enable Tethering then click "generate". Install the MobileConfig you just created then reboot.
Once your iPhone has restarted go the settings- general- network-cellular data network then change the cellular data apn to "orangewap", then go to the mms section below and add
MMSC:
http://mms.orange.co.uk
MMS PROXY: 192.168.224.10.8080, then come out of settings reboot then you should be able to send and reciece MMS! Obviously ensure mms is enabled in the messages section of settings!