I was being a bit sarcastic but seems to have gone over some heads.
On prepaid, every time you recharge they give you some ridiculous amount of free data, sms's or airtime. Granted its limited for the day, week, network, etc.
As far as contracts vs prepaid there is a lot in it. Vodacom for example doubles the airtime/data/sms if you take a sim only contract (sans rollover). You also can save 1000's on the device by buying it outright. MTN charge only a small amount extra for the handset over what the cash price is, but airtime/data/sms are not doubled. MTN customers can buy their data from Axxess cheaper than MTN and it has a 3 month rollover. Afrihost offers MTN customer voice and data with a 12 month expiry?
Prepaid has longer expiry than contracts. Contracts may roll 3 months, where as prepaid is valid for year +. Also look at how you use your phone for voice. If you recharge strategically you can just about get 50% free calls during the day. Example is if you recharge Vodacom with R50, you get R25 free any network airtime for that day. Also look at the advertised per minute charges. Some networks offer discounts on those rates depending on where you are (low traffic on tower) and what time of the day it is or day of the week.
Advantage of contracts (so the networks say) is that they have priority on busy networks. Disadvantage of prepaid is all the spam sms's the networks send you.
Then there is the cost of a sim swap should you need it. prepaid is very easy, go buy a 50c sim almost anywhere and do it over the phone. Contract customers need to go to a network store and pay R80+ for the same sim card.