It took quite a bit of fiddling, but here are the settings I used with SwirlyMMS to send/receive MMS messages via my non-iPhone O2 contract. Click the thumbnail for a better view.

I found this page at the swirly site only got me partly there. I also needed the APN, Username and Password stuff which I'd found in the process of trying to figure why EDGE didn't work on my iPhone - that was due to me NOT having the data bolt-on package.