Avoiding the unneccssary payment of tax is part of a corporate's obligations to its shareholders. Evasion of tax is illegal.
Many companies see it as avoidance as they can get away with it.. What MTN is doing is evasion because while it might have been dark art skills.. This loophole was closed in March 2015? And trying to hold the country rand son should result in gov slapping them on their head with the investigation into contract re pricing..
In Fact I suspect if they pursue this line of argument expect MTN to pay the most fines and ICASA to take up a lot of QA claims against them. In the end.. Much like road rules, eTolls and the idiot drivers in Gauteng, what's legally signed into law you have to obey as that's part & parcel of using the road or in this case doing business in SA or face consequences.