I offer to you a German vodafone prepaid sim-card. If you want to spend your vacation in Germany it is good to have a German sim-card with a German mobile telephone-number There are  EURO 20 booked on the sim-card. And thats are the points for a German sim-card:

No roaming-costs in Germany for calls to mobile-phones and to the fixed  telephone network.

Cheap calls within Germany, only 9 cent to all German networks when in Germany

Usable in all contries of the European Community, incoming calls are free, outgoing calls within the foreign country are as expensive as in Germany, data packages can be used in all EU countries.

If your friends wants to call you on your German telephone-number tell them the number before you start your holidays. You will not pay any charges for the call of your friends to the German number when you are in Germany.

When you buy this card,it is pre-registrated. So I need not any information to activate this card.

I will also send you an English translation how to use the sim-card.