Are they not paying the respective networks the due termination fees? If so, I see nothing prejudiced going on. They are not using anyone's international gateway, the only thing they utilise is the interlink. If EWZ & co. think their current termination rates are too low, then they should raise them across the board (including local calls). Nothing is stopping any of them from leveraging the cost-effectiveness of IP. Besides, international call routing (and calling cards) predates IP telephony.
Let the companies fold, if they can't keep up (1 is looking pretty sickly these days). I'd be cheering very loudly if a (new) company were to do to Econet what Econet did to the PTC. If you remember, lot's of noises were made back in the day to protect the PTC (unsurprisingly, it involved lot's of anti-EWZ legislation. We all know how that turned out)