Is it even implementable?
What hasn't been clearly answered is whether or not the proposed restrictions on foreign visitors are even implementable. At a very high level, it would be necessary to know the IMSI number of each subscriber roaming in SA, and each of the three mobile networks would need to somehow keep a record of all IMSIs that are permitted to roam. Then the question becomes how to determine for how long a particular subscriber should be permitted to roam - this is especially tricky with subscribers from countries who do not require visas, and who might have open-ended air tickets.... Additionally, this would probably preclude travelers who are in transit at an international airport from roaming in SA.
It might be interesting for some of the engineers from the GSM operators to comment on this. I for one do not believe that these proposals can be technically implemented at a reasonable cost.
Tracking the IMEIs of all phones active in SA is also a futile exercise, since many travellers buy phones overseas and use them with South African SIM cards. That just creates another exercise in futility.
If this legislation does however succeed in preventing criminals from using mobile phones to commit crimes, it will just prompt them to use alternative technologies. Then again, forging South African ID documents, drivers licenses and passports is so easy, so why bother ....