You don't really win, as you get free minutes with your contract as well.
I got my Desire HD from MTN on a Anytime 100 contract @ R249 a month (no pay-in), which works out to : R249 X 24 = R5976 + R100 worth of airtime for 24 months = R2400 worth of airtime.
So....if my calculations are correct : R5976 - R2400 = R3576 is what I'm actually paying for the phone.
but like how much data you using every month extra than just the R100 airtime ?