Solomo pro is also attractive, as they have the same cheap international rates to Belgium as Fonic, but the fact you wanted to buy the SIM "on the spot" hindered me from recommending them to you, as they sell their SIM online only. Also as Motel75 mentioned, there's no data option beyond those € 0,24/MB and they use the eplus network, which is inferior.
On the other hand solomo pro has cheap roaming rates (incoming calls within Europe for € 0,10-0,15/min) and it includes a free VoIP-account, which offers parallel call (mobile phone and VoIP ringing simultaneously) and cheap outgoing calls to solomo subscribers for € 0,05/min (including your own solomo SIM). The VoIP-feature allows you to be reachable on your German mobile phone number anywhere in the world for free, where you have internet access (just need a VoIP-device or -software). Further if you have some VoIP-device supporting multiple VoIP-accounts and VoIP-forwarding (like a Fritz!Box) you can forward incoming calls from some DID-number through solomo's VoIP-account to your solomo SIM for € 0,05/min.
solomo does ship SIMs to Austria, Belgium, Czech Republic, Denmark, France, Netherlands, Poland, Switzerland and Spain. They usually send SIMs the next day and should arrive in the named countries within 2-3 days.
If you order through
this link you'll get an additional credit of € 5. So with this month's promotion you get the SIM with € 10 of credit for € 5.