I have recently got a Blackberry Curve 3G on a 24 month contract and when I go to view my bill online I get this message...
"For some reason we do not have a pay monthly online bill associated with the "username and password" you have signed in with.
To view a pay monthly online bill you will need to have set up a pay monthly mobile phone account and when you set this account up you would have been given, or chosen a username and password. You need to use these original 'sign in' details to view your bill online."
However, I had already signed up to the O2 website with my previous phone which was PAYG and had the same number. My previous phone was a Sony Ericsson w580i if that helps.
Sorry if this doesn't make sense.