Can't update apps on iPhone 4

Hi,

since 3 days I haven't been able to update apps on my iPhone 4 (english translation from German : "connection to iTunes Store not possible"). Purchasing apps is still possible on the iPhone, updates work via PC and iTunes. It's just pretty tedious to connect evertime to a PC just for checking for new updates. I have the iOS 5.1.1. installed.

iTunes support team gave me advices like "switch iPhone off and on" and "sign off from the Apple store and sign on again", which were of course first things I tried.

I hope you experienced guys can give me some hints how to get rid of the problem.