AP Photo

AFRICA’S “mobile decade”, when telephones at last reached most corners of the continent, has meant a huge improvement in the lives of the poor. But quantifying it is hard. How useful can a mobile phone be to someone living on less than $2.50 a day, the World Bank’s standard benchmark of poverty? Researchers in Kenya have given a partial answer. They find that people will skip a meal or choose to walk instead of paying for a bus fare so that they can keep their phone in credit.