From TechCentral's live blog of the JHB launch event:
Not quite as good as the "data only" sims but not bad. If you're going to want to use your phone as a phone and as a modem probably still worth it to get a 2GB/mo sim and use prepaid airtime.
10.53
“As of Friday, we will sell data bundles in the stores. For R50, you get 100MB, for R100 you get 250MB, for R150 you get 500MB, for R250 you get 1GB and for R400 you get 2GB. These are top-up rates on postpaid contracts.”
Not quite as good as the "data only" sims but not bad. If you're going to want to use your phone as a phone and as a modem probably still worth it to get a 2GB/mo sim and use prepaid airtime.