1. Legal Intercept - This is already law and most - if not all - OTT voice and messaging players don't comply.
3. Taxation - OTTs like FB derive a crap-load of revenue from advertising. That is how they can give the service for free. They are selling YOU as the product. All this money flowing out of SA is making people sit up and take notice.
These sound like the governments problems, not MNOs.