In MHO, the price drops by MTN and Vodacom are mere marketing strategies. Wow, bandwidth at 19c/MB... but have you seen how much you have to buy first? And what you don't use you loose...
Unless you are only using 3G or EDGE for internet access as you are permenantly on the move then ADSL or Wifi are better options.
If you are like me who only uses 3G or EDGE when he travels or is needing to quickly change a setting on a clients website whilst having a beer at your local Dros, then Virgin Mobile is perfect. I changed cos I used to spend over R200 per month on GPRS (cos Vodacom says the EDGE doesn't work in SA).
Now I pay over R50 per month for EDGE... VODACOM is just another word for telkom...