I have exactly the same problem, I am in the UK on the O2 network. It is definitely a network provider problem, I can tell you exactly when this problem started for me. In the UK there was new legislation brought in to block the Pirate Bay domain.
Ever since the the carriers in the UK had to update their settings on their mobile devices this problem started and it seems to be absolutely no way to get it resolved.
I have tried, in vain, to get O2 to do something to this problem that they are unable to do so.