Take a minute and guess what the most visible piece of advertising is in Tanzania. What product do you suppose it is for? What company logos are most prominent?
Coca-Cola?
Some local beer? (Kilimanjaro beer. They got the marketing to tourists thing down)
Nope. The ads you see plastered on every store in Tanzania are for cell phone carriers. It turns out that 4 carriers are in brutal competition to capture the market. These are tiGO, Celtell, Zantel and Vodacom.

(did GoLoco steal its logo from tiGO or the other way around)
Cell phones the most revolutionary thing to come to Africa in decades. It was always too expensive to run copper lines so not many people had them. Now you get crystal clear coverage right in the middle of the Serengeti.
It isn’t cheap though. In Tanzania you are charged for outgoing calls by the second. Everything is prepaid, and text messages are free.
This is a country where people walk miles just to go to the market to trade goods. Not many people have cars and the ability to coordinate over distance changes everything. As such, everyone wants to have a phone and companies are more than happy to compete for their business.