I would imagine Mobile Payment Option has to be supported by your carrier first. When I got my Lumia 900 it defaulted to that and the first time I went to buy and app it asked me how I wanted to pay. Again it sounds like something your carrier has to support first specifically for Windows Phone. You can try calling up their support line and see if they know.
Originally Posted by GT2010
I do not know much about how South African mobile systems work but what I used to do years ago is I would buy those pre-paid Visa gift cards and they would act like credit/debit cards most of the time and I would use that.