Prepaid SIM card in Shanghai

Hi,
Anybody know where I can buy a prepaid SIM card in Shanghai?

I would like to buy a 3g/4g prepaid sim card to use it mainly for internet connection and local voice calls.
I searched a lot and all I could find are old posts related to the subject.

We (my work mates) use iPhone 4 and Samsung 2S.

Which sim card should I get and where to purchese it? International phone calls to Germany should not be expensive...

I would like one that gives the best coverege in the areas of pudong/puxi.

Thank you very much for your help!
Tobias