I suppose this may depend on the SIM, but generally these can be quite expensive to call (stupid, I know). Without looking I would say that they would be at least as expensive (if not far more so) than normal geographic landline numbers.
The reason I say this is because even with postpaid contract arrangements these numbers are never included in the bundles of minutes you have. This is probably because the network operators are aware that people want to call them for call-through services etc
Take a look and see what's about - happy to help in any way I can
