ft.com - ©Dreamstime Number of millionaires 5,000 Percentage that use mobile money 74 per cent Nairobi’s shiny new malls and snazzy restaurants jostle for attention alongside the sprawling slums that house more than half the city’s population. But the “Silicon Savannah” in Kenya’s capital is springing to life, buoyed by the success of mobile phone money transfers and Kenyans’ enthusiastic adoption of social media.