Not necessarily. The essential value is what is average rate which any specific operator receives per minute. I mean, what if a large part of the overall traffic are cheap on-net calls (=much cheaper than 10 ct/min). As long as the whole thing remains within the home network, that's OK. But what should happen when the SIM is roaming in a foreign network with the termination rate 8 ct/min.? If the call to that SIM comes not from the home network, the operator receives 10 cents which is probably enough to cover forwarding abroad including the termination fee of the roaming partner. But if not, i.e. the call comes from the home network at the on-net rate, let's say 5 ct/min who will pay the difference? Differing the inbound rates depending on the origin of the call is technically possible, but would it be acceptable by customers? Of course, my example doesn't exclude free incomig calls since losses on the inbound calls may be compesated by profits from outbound calls. But such pricing may force some "fair use policies" like limiting the volume of incoming calls or the inboung/outbound ratio...

Poland: "the Big Three" i.e. Era, Plus and Orange and their MVNO's take 0.40 PLN and Play takes 0.65 PLN. At the current exchange rate it makes about 0.11 and 0.18 EUR, respectively. The rates above are exclusive of VAT, of course.

Have you found better rates to Poland mobile? Probably yes. How do they do this?
http://en.wikipedia.org/wiki/Fixed_cellular_terminal
Of course, it's illegal here, not by the national telecom law, but by the operators' ownership rights - Polish SIMs are formally properties of the operators and FCT usage is a violating of T&C's of someone's property :-).
The same trick applies to many other countries :-).

Voicetrading charges:
Poland (Mobile) 0.0489
with ability to set CLI, so they are probably not using a Sim box.

I understand the working of a Sim-box (the idea behind it), but I still don't understand how Betamax has so many rates that are below 'the possible'.
I can 't believe that they deliberatly loose money to make money on other destinations. Have they found holes in the system? Possible, but how can they keep doing it for such a long time without getting caught?

Maybe Andy knows more ?