It won't work until tomorrow when the new MMS service is officialy announced. Settings can be downloaded OTA from the new MMS section on the O2 site. If you are on a tariff greater than £25 a month you will get 150 free MMS a month when the current offer finishes, not bad!
If you are on an old Genie contract, you will need a bit of luck getting O2 to enable your sim for MMS. Apparantly they have insturcted all staff not to do it.
I changed my tariff, I know that sounds stupid, loosing my:
600 SMS
Unlimited WAP
100 Anytime minutes
for £12.50 a month, but the girl made a mistake! She's given me:
500 off peak mins
50 cross network mins
500 SMS
500 min WAP
for £15 a month. I'm a happy guy! I got the tariff so cheap because I was a sim only customer(!) when I first joined way back last year. I can also still ring back up tomorrow and get my upgrade to an new handset and still only pay £15!
Still can't send MMS though, I get the GPRS 'G' but then get a message saying 'User Barred' :(