One of the first things that strikes you about the chaotic East African metropolises of Kenya, Uganda and Zimbabwe is the blanket of adverts for mobile phone companies that covers them, from the walls of the immigration hall at Harare airport, to the rickety shacks that line the dusty streets of Kampala. Where official signage is unavailable, DIY versions are painted onto the roofs and walls of houses and small businesses. Stores selling mobile phones are rarely more than a few short steps away…