Here follows the telling of some personal experiences, also known as ranting.
I've registered online at myistore now, wish I did that long ago. However, I pre-register with MTN within 2 hours of them opening up pre-registrations, haven't heard a peep since. Vodacom did actually call me, but it seems I managed to pre-register for completely the wrong colour and size, so the call ended with me having to wait for the next round of stock.
I went to each Vodacom we walked past in three different malls and they all have the same response: "Errm, umm... No we don't keep the 64 and 128GB iPhones here because of the robberies. We need to order it for you which takes a few days. Oh, we don't know if the warehouse actually has stock, so...". So no Vodacom can give any sort of time estimate and none of them offered a waiting list. I fully understand that they don't want to keep stock now, except that the 16GB isn't that much cheaper and they do keep that. I don't want to beg for a waiting list, we did that last year for my wife and we got a really strong vibe from many of the MTN guys that they really just write your name on some random piece of paper to make you go away. Each of them use a different piece, so you immediately know that nobody is going to go through all those lists later on. At some point we also got the idea that they are purposely holding stock for friends and family (or maybe for money, never actually thought about bribing them).
Then I decided to try the iStore in Canal Walk. First time I ever had a reason to enter an iStore. The woman who helped me also could not give me a time estimate, but did offer to take my name and number and was far more responsive, friendly and knowledgeable than anyone we spoke to at network stores before that. So with that and the online registration, I'm just patiently hoping to get in on one of the batches soon.
It would really be great if there was a lot more transparency about when stock arrives and how many people are in the queue before you, but they probably have reasons why this is not very public info.