I am having the same issue. Full bars and 3g icon but nothing works (Safari, email, Foursquare, Facebook).
I also have the issue (which I think is linked to this) of iP4 dropping data connection during the call - see here
https://forums.macrumors.com/threads/956138/
My battery life is very poor due to this as I think it keeps dropping 3g and then looking for it constantly.
I have a bumper case so it's not linked to the antenna issue.
My girlfriends iP4 is perfect and doesn't do that when both phones are side by side. Also my facetime calls to her fail most of the time but she gets through no matter what.
I've done everything from resetting network settings to changing sim cards.
I am on Vodafone in the UK if that helps.
Genius appointment tomorrow...