Grant Gibbs designed the Hippo Water Roller to give poor, rural South Africans an easier way to collect water. The Hippo is a plastic tank which doubles as a wheel, with a handle. It's easy to fill and easy to pull over rough rural terrain, even by children. It's an ingenious solution and as it turned out, people love the product, but will not pay for it. Despite its success as a development aid project, it was always acknowledged that it would not be a commercial success.

On the other hand, an interesting fact that emerged from the 1999 ICSID Interdesign, hosted by the Design Institute of South Africa was that the same disadvantaged people would pay someone to deliver water to their homes, rather than fetching it themselves from a communal tap. It seems that time is as valuable at the bottom of the pyramid as at the top.

At the opposite end of the technology spectrum, mobile phone company MTN has become one of the fastest growing telecoms companies in the world by expanding into risky markets in Africa. Some stories tell of people traveling for days to spend several month's wages on a phone. It's easy to assume that the explosive growth of mobile phone sales in Africa is simply a matter of usefulness; people are able to communicate where previously they were not. However it's possible that this is only part of the reason.

Aside from the inevitable calls to far away family and the crucial contact number for an itinerant handyman, mobile phones are used to arrange a lift, a party or for other social events that would have otherwise meant a possibly fruitless walk. In other words, the phone provides convenience, just like the service of water delivery.

C.K. Prahalad has pointed out that developing world customers are savvy and value-conscious. That's true, but there could be more to their discernment than that. Maybe the difference between the Hippo Roller and MTN is that these markets need not only great usefulness but also great convenience before they'll open their wallets. Add the possibility of earning extra money and you may have a winner.

Tasos Calantzis