I'm also South African and I'm with Nedbank. When I wanted to start purchasing things online and apps for my Android (sacrilege, I know!), I simply went to my nearest Nedbank branch and told them I wanted this functionality, but still on my debit account. Back then, I only had a savings account and they told me it would be impossible without a cheque account. At first, I was concerned about this, but after they explained to me that it would function like a normal debit account, I went with it. I opened the new cheque account and received my cheque card linked to the account, and since then haven't had any issues using it on the Windows Phone store to purchase apps (oh so many apps... It's scary how much I've spent on them!)
TL
R
You need a
cheque card. Just go ask your bank about acquiring such a card and how it would influence your accounts (hopefully, you don't need a new account. But like I said, setting up the new account and getting the card was super quick and easy at Nedbank.) Don't know how the Maestro, Mastercard or Visa-electron stuff works, but mine is a straight-up Visa card.
Hope this helps!