O2 Question (Nokia 6600)

I've just upgraded my phone from a 7250 to a 6600. I called O2 a long time
ago and asked them to activate MMS on my sim/mobile. On my 7250 it all
worked fine. I've applied the same settings to my 6600 however I am unable
to receive or send MMS and further to that the GPRS WAP is dodgy! What I
mean is, it will let me surf through O2's active portal but it won't let me
connect to any other WAP site!? Also, surfing O2 Active it told me it
doesn't recognise my phone or number (can't remember which now).

Any ideas what the problem is and how to get around it?

Cheers
Chris