Africa has been called the first mobile-only continent. Mobile phones double as payment devices, flashlights and music players. Songs from far-flung locales are swapped via SIM cards on city streets and at dusty truck stops, and a single cell phone can provide a plethora of music from all over Africa. Far away in Portland, Ore., Christopher Kirkley, a self-described gentleman explorer and rogue ethno-musicologist, currently makes a living releasing music from Saharan cell phones. In 2008, Kirkley went to West Africa to record folk music. …