Ms Wokhwale prospered because being able to make and receive phone calls is so important to people that even the very poor are prepared to pay for it. In places with bad roads, unreliable postal services, few trains and parlous landlines, mobile phones can substitute for travel, allow quicker and easier access to information on prices, enable traders to reach wider markets, boost entrepreneurship and generally make it easier to do business. A study by the World Resources Institute found that as developing-world incomes rise, household spending on mobile phones grows faster than spending on energy, water or indeed anything else.