Basically, I am ignoring your question and telling you to buy a global SIM before you go and not get a German SIM card!
You might want to check eBay and look up ekit's 'Home and Roam Travel SIM card' OR 'ekit Passport SIM'.
The H&R costs slightly less and has better rates calling an EU mobile phone. Ekit has two different seller names. One is US based and the other is UK based. I have bought from both with no trouble [except you might want to make a notation in the message to seller box repeating you usa address information.{I just had an issue with the UK seller and this would help them.}] The H&R also has a less expensive price.
Both have free call receipt for all the countries you listed to the UK number. Both now have a US and UK number. Do a little research now and you can buy it and have it before you leave.