Mobile phone use has grown rapidly and globally over the past decade, with some 6.84 billion phones used worldwide in 2013 compared to just over 4 billion in 2009. Although initially restricted to the rich, mobile phone ownership and use has filtered down to the lower socioeconomic classes and spread to poorer countries, which currently exhibit higher rates of mobile phone penetration growth. Mobile phone ownership and usage patterns remain different, however, among the rich and the poor. Richer people are more likely to own more expensive phones with a wider array of functions, for example, so-called smartphones, whereas poorer people are more likely to own cheaper phones, to use them less often, and to use them in more limited ways.

The spread of mobile phones ...