Purchasing South African SIM Cards
Some advice - the SA authorities have introduced a scheme whereby all purchasers of SIM cards have to prove their identity (known as RICA).
So - when you go to purchase one, make sure that you have your passport with you - if you are purchasing directly from one of the major providers (particularly Vodacom), they will almost certainly ask for prrof of an SA address too - a letter from a hotel is deemed sufficient. If you don't have this, then a solution is to shop around some of the secondary providers (department stores, major fuel stations etc) - they don't seem too fussed so long as you have the passport.
We fell foul of this and wasted a full day getting two SIMs!