Just a tip for anyone purchasing a Fonic SIM:
If you activate your Fonic SIM online at
https://www.fonic.de/selfcare/servlet/ActivationInfo, there will be a field called "Mobilfunknummer/Aktionscode eingeben". If you enter another Fonic customer's phone number there, you and the other Fonic customer will both get an additional bonus credit of € 5 due to their customer referral program.
So ask some Fonic customer (e.g. our fellow forum member
VladS) for his number before activation.