Instant cash (Image: Tony Karumba/AFP/Getty)

WITH smartphones taking the world by storm, a phone that can only send and receive voice calls and text messages may seem like a relic from a bygone age. Yet in East Africa, simple phones like these are changing the face of the economy, thanks to the “mobile money” services that are spreading across the region.

Using the text-messaging capability built into the GSM system used by most cellphone networks, these services allow people without a bank account or credit card to use their phone as an electronic wallet that can be used to store, …