Mobile Data for Multiple European Countries
 

I'm from the US and I'll be in Europe for two weeks and using an unlocked iPhone 4 (not 4S). Countries visited will be:

Germany
Croatia
Italy
Belgium

We'll be landing in Munich, Germany. Is there a provider I could go with and pick up a sim upon landing in Munich (or any surrounding area)? I don't have enough time to wait for a sim to be mailed to me while here in the US.