If you haven't, I would recommend you look into m-Pesa. In some countries (not all countries), M-Pesa uses USSD (like Tanzania I think).

Overall, some of the solutions for payments and banking being implemented in some developing countries is quite different than what most people in the west are used to. M-Pesa is one of them, but in countries like India, online wallets are starting to gain traction too.

Most people in developing countries don't have credit cards, let alone being comfortable using them online. So a lot of people in India still use the 'Cash on Delivery' model, which isn't very much prevelant in the west, and other solutions like 'Netbanking' (in which the shopping site redirects you to your bank provider's site, you log in, and through the bank provider's site you do the payment, and then it redirects to the shopping site's payment confirmation page ; In other words, you haven't used a card, you've just paid directly through the bank) are also there.