Over the last two decades, cellphones have ushered in a communications revolution in Africa. The entire country of Mali, for example, has just 120,000 landlines to serve a population of 15 million. But as of 2012 there were enough cellphones in service in Mali for every man, woman and child. The spread of cellphones in this way has driven innovation across the continent. M-Pesa, a text-message-based money-transfer system, has made financial services available for the first time to millions. Another enterprise tells rural farmers by text what their crops might sell for in distant markets; mass-texting campaigns have helped promote major public health initiatives.

Yet for many Africans, the phone is not merely, or even principally, a communications device. You can see this on the sun-blasted streets of Bamako, Mali’s capital, where a new kind of merchant has sprung up along Fankélé Diarra Street. Seated practically thigh to thigh, these vendors crouch over laptops, scrolling through screen after screen of downloaded music. They are known as téléchargeurs, or downloaders, and they operate as an offline version of iTunes, Spotify and Pandora all rolled into one. They know what their regulars might like, from the latest Jay Z album to the obscurest songs of Malian music pioneers like Ali Farka Touré. Savvy musicians take their new material to Fankélé Diarra Street and press the téléchargeurs to give it a listen and recommend it to their customers. For a small fee — less than a dime a song — the téléchargeurs transfer playlists to memory cards or U.S.B. sticks, or directly onto cellphones. Customers share songs with their friends via short-range Bluetooth signals.

This was the scene Christopher Kirkley found in 2009. A musicologist, he traveled to Mali hoping to record the haunting desert blues he loved. But every time he asked people to perform a favorite folk song or ballad, they pulled out their cellphones to play it for him; every time he set up his gear to capture a live performance, he says, “five other kids will be holding their cellphones recording the same thing — as an archivist, it kind of takes you down a couple of notches.” Kirkley has since released compilations of music from what he has called “digital Bamako” and other places across the Sahara, as well as solo albums by artists who appeared on them.

What make its existence possible are not smartphones but so-called feature phones, which do little more than make calls, take highly pixelated pictures and play music. And yet they are indispensable. In 2013, when French troops intervened in Mali to help fight Islamic militants and Tuareg rebels, I arrived in Timbuktu not long after its liberation. The cellphone network had been down for days, so I did not bother to charge my phone. But every night, when the gasoline-powered generators in town rumbled to life, a long line of people formed to charge their cellphones. Why, I wondered, would anyone need a cellphone without a network connection?