There's also an interesting company called
qipu.de which pays back a percentage
in cash for each purchase at a lot of online shops including Fonic. For a
Fonic SIM they would pay you € 5 by bank transfer or PayPal (-2% PayPal fees) after 8-10 weeks. I've made use of this service a couple of times and I consider the company pretty serious, since it was founded by a guy called Fabian Spielberger, who runs
mydealz.de - probably Germany's most famous bargain blog.
However qipu works only if you purchase your Fonic SIM online and that again requires a German bank account for the initial payment.