They (the browsers I listed) need a GPRS Internet Access Point & won't work with a GPRS WAP Access Point (except WebViewer).
GPRS Internet Access Point tariffs are usually higher than with WAP Access Points.
Also, some operators/carriers (or specific subscription plans of theirs) may not provide access to any Internet host/server through their WAP Access Point (requiring you to use the more expensive Internet Access Point instead, if they offer that at all).
Ask O2 what their PAYG (whatever that is) Internet Access Point settings are (if they're not on their website).
PAYG is Pay As You Go, you top up your phone with money before you use it, so I probably think there is no other option but WAP access points through the Dial up option :( Oh well, i'll have a look at that Webviewer id if had a demo