This is an interesting topic, we can make a general statment that poses a fundamental challenge to this problem. How can mobile providers restrict certain users from using interent untill the user pays a certain amount of money?
The package the op is using is rather strange, i've never heard of a mobile providers allowing access to a certain website only? Where i live and i think this can be generalized world wide, you have internet packages (eg. 1gb, 5gb or unlimited) each and every package has a certain price.
In the end, i think the problem lies in the dns settings, i've done some searching and i found this link. It could hold some answers.
http://blog.varunkumar.me/2010/09/how-to-change-dns-server-of-3g.html?m=1