Back in the mid-1990s—the Dark Ages—I was living in a semi-rural area on the slopes of Mount Meru, just outside Arusha, Tanzania. Every now and then I had to make a phone call back home, across the world.

This is not an easy thing to do, I often thought to myself as I headed out into the neighborhoods to inquire about using one of the few phone lines at houses near mine. Often, these lines would be broken, or working spottily, and it could take weeks to get a repairman out to find the place where there was a problem. Moreover, the calls had to be arranged in advance so both people's ears could be physically connected to the line that ran under the sea.

Usually, I would end up knocking on the door of a business in town (owned by friends of friends), trying to be unobtrusive as I heard the crackly sound of the voice of the woman I would later marry. But our words seemed to run into each other along the way, and we each had to wait a minute to be able to hear the other. In the lag, the distance seemed tangible.

These days, when I'm in Africa, I tell people this story and they laugh. They laugh as if they can barely remember those times. They laugh like I was telling them I used to hunt with rocks and start fires with sticks. Because technology in the developing world has changed so much and so fast that it's hard to believe unless you see it yourself.

I did see it last year, while I was taking a bus across West Africa. As I sat looking out the window at the dusty trees scattered around the Sahel, somewhere in the middle of Burkina Faso, I took a phone out of my pocket and called my wife. This time, the sound was clear. There was no delay. It was almost like she was sitting next to me.

I may have been the only passenger dialing America, but I was far from the only one with a phone. And while not everyone can afford this kind of technology, in the last decade cell phones have become shockingly common. There are now 415 million mobile subscribers in Afr...