I am on pay as you go (no idea of its simplicity, just a sim i bought a few months ago as my old sim wasnt 3g. The mobile internet doesnt work at all at the moment.
If you're pay as you go any chance to can copy your settings in the different APNS? (should be one for internet and one for mms *i think*), n ot sure about the passwords tho.
I have e-mails o2 to see what they say, but remains to be seen if i get a reply.
I'm not on payg, got the 12month £15/month simplicity for smartphones (300mins, unlim txt & internet) contract.
sorry can't help you with the settings for payg.