Cell phones are an example of what is sometimes now called leapfrog technology, a product that allows developing nations the benefits of a reliable and extensive communications network without the heavy investment in fixed-line phone infrastructure. Mobile phones, along with Internet access, are part of a communications revolution that is helping boost income and stop the spread of disease in emerging economies. VOA's Bill Rodgers has more in this second of a series on technology in the developing world, with additional reporting by Cathy Majtenyi in Rwanda, Wakil Ehsass in Afghanistan, Nico Colombant in Liberia, and Ahadian Utama in Indonesia.

Abdul Wakil owns a dry goods store in the Afghan village of Daw Koo, about 40 kilometers north of Kabul. He says his cell phone has made all the difference.

"We used to go all the way to the city to order products, now it's only a phone call away and the costs are much less," he says.

The International Telecommunication Union says 72 percent of Afghanistan's population is now covered by a cell phone signal. By contrast, fewer than one person in a hundred has a fixed telephone line.

The rapid spread of cell phones in developing nations like Afghanistan is the result of several factors.

"There is a combination of being exposed to the technology, allowing it to get into the country, and then ... having an environment in which it can flourish. And that means having the regulatory environment, it means having a population that is able to take advantage of it," explains Andrew Burns, a lead economist at the World Bank who is the main author of a study on the spread of technology in the developing world.

Cell phone use worldwide has increased as more countries have opened up their state-owned telephone systems to allow private companies to build cellular networks. By the end of 2006, 68 percent of the world's cell phone subscriptions were in developing countries.

Burns says ease of use has been key to the cell phone's rapid spread.

"You don't have to be literate, you don't have to be numerate, you don't have to be able to do mathematics or anything particularly complex," he says. "You have to be able to type in the numbers, and it is extremely empowering."

And financially empowering as well. Mobile phone banking is rapidly becoming popular in developing countries, where many people do not have bank accounts.

In Kenya, a low cost cell phone service called M-Pesa allows people to send and receive money via text messages. The service is popular because it eliminates the need for people like Daniel Rohio to travel long distances to deliver or receive cash.

"If I wanted to send money to my mum at a particular time or my grandmother, she cannot receive that money and would have to wait for maybe at least one day or two days. So I have found M-Pesa a little bit easier to send money to them right now," says Rohio.

Cell phones also are proving to be a medical tool, helping to halt the spread of diseases such as AIDS. In Rwanda, health care workers in rural clinics use cell phones equipped with a special software developed by the U.S. company Voxiva. The software allows healthcare workers to enter data into cell phones about drug stocks and AIDS patients, and then transmit this information via text messages to health officials in Rwanda's capital, Kigali.

With this information, officials can better monitor the spread of AIDS and deploy medical resources to clinics to treat the disease. Jean Luc Hassan Kavumu, a nurse at a rural Rwandan clinic, says the system has helped patients.

"I used to travel to Kigali to take information and while I was gone, there was no one to attend to the patients," says Kavumu. With this system, he says, he is now at the clinic all the time.

Yet in some nations, poverty is so great that cell phones have yet to make much of a difference.

So while cell phones have allowed developing nations to skip fixed-line technology, experts say they cannot, by themselves, bring about economic development. Reliable sources of electricity, advanced road networks and other infrastructure must be in place, they say, for developing countries to experience sustained economic growth.