i have the same problem but on orange.
on o2 you can manually enter the settings:
Pay Monthly
To change your data settings:
From the main screen of your iPhone, tap Settings > General > Network
Tap Cellular Data Network.
Under Cellular Data, tap APN and change idata.o2.co.uk to mobile.o2.co.uk (o2 needs to be written with a letter o, not a zero). You dont need to change your username and password.
Ignore the APN box under Visual Voicemail its not available if you dont have an iPhone Pay Monthly tariff.
Under MMS, tap APN and change idata.o2.co.uk to wap.o2.co.uk (o2 needs to be written with a letter o, not a zero). You dont need to change your username and password.
Turn your iPhone off and on again.
taken from here -
http://shop.o2.co.uk/update/settings.html
i'm on orange and can't do it manually and stuck waiting for a carrier update!!