Go with Vodacom
1) Get a 3G/HSDPA card. It goes for around R2500, but I got mine on bidorbuy.co.za for less than half that price.
Be careful not to buy a 3G card. Insist that it be the 3G/HSDPA which allows for faster access.
2) Get a 64k simcard. Vodacom will not give you a 64k card, and the ones you get are 32k. You need to buy a '32k' simcard, use it for sometime, and then simswop it for a 64k simcard. This costs around R75
3) 500mb costs R189, 1gig costs R289, 2gig costs R389. You need to buy airtime more than this. It gets a bit tricky, as Vodacom sells R28, 55, R110, R275.
Do the combos to get to an amount.
4) Put the simcard in a phone and register on
www.vodacom4me.co.za Log into vodacom4me.co.za and convert the airtime into a data bundle
5) Install the software, and blaze away.
This is with Vodacom, don't know how the others work.
BTW, Vodacom data bundles only last for 30 days. You forfeit what you don't use.