IQUITOS, Peru -- A few miles downriver from this city in the western
''This is what they call the `telephone of the jungle,' " says Alvarado, a tricycle taxi-driver and tourist guide.
Moments later, as children of the Bora Indian tribe come bounding down the path to answer the ''telephone," Alvarado's belt begins beeping: It's his cellphone.
Iquitos and nearby riverside hamlets are among the more remote outposts in South America's expanding mobile phone system, part of a global network that is beginning to penetrate even the poorest and most undeveloped corners of the world.
For millions of people living in countries where getting a fixed phone line remains a bureaucratic impossibility, the cellphone revolution has allowed them to leapfrog from archaic forms of communication straight into the digital era -- and that is changing the fabric of their daily lives.
In East Africa, the mobile phone has brought a first, tantalizing taste of modernity to people who live on less than $10 a day. In China, the world's biggest market for cellphones, they are embraced by rich and poor alike, a tiny pocket computer with which to surf the Internet, play video games, or even do banking.
Here in Iquitos, where speedboats and lumbering old fishing craft ply the brown, wide waters of the Amazon, fishermen grab the wheels of their vessels with one hand and their cellphones with the other to check the price their catch will fetch at markets downriver.
Alvarado uses his mobile phone to round up clients for his tricycle taxi. And earlier this year, it beeped with the most important call of his life.
''My mother-in-law called me from the delivery room," Alvarado recalled. His wife had gone into labor with their first child, and he raced to the hospital on his tricycle. ''We all thought we were going to have a girl, but it turned out to be a boy."
He flashed the news from the hospital to his sister in Lima, Peru, via his cellphone, the kind of call that might seem routine in the United States but which still carries for him an aura of science-fiction.
The number of cellphones in Latin America has tripled since 1999, and one in five people now owns one.
In Peru, as in many other countries in the region, there are more cellphones than fixed phone lines.
Today, the world's fastest-growing cellphone markets are in places like Iquitos in rural South America and in sub-Saharan Africa, despite widespread poverty.
''My cellphone gives me an 'address' just like any other businessman," said Baruwani Mbabazi, a money-changer who is part of a brisk trade in US dollars in Kigali, the Rwandan capital. His $20 purchase of a used cellphone has liberated him from having to stand on the street waiting for customers.
''I can't imagine my business without it," Mbabazi said.
Rwanda's cellphone boom has followed a pattern typical of many developing countries. It now has more than five times as many cellphones (134,000) as fixed telephone lines (23,000), according to the International Telecommunications Union.
As in Rwanda, people elsewhere across Africa are coming to appreciate and rely upon the magic of the cellphone -- communicating with a distant friend while under a baobab tree in Mali, for example, or on the Kenyan savanna.
In Senegal, farmers use them in their annual, age-old battle against plagues of locusts, calling each other and the authorities to keep track of the progress of insect ''hopper bands."
In Somalia, men in loincloths flash their cellphones as they guide camels to port. Masai warriors in Tanzania pull phones from their red ''shuka" robes to call gem brokers when they find glimmering purple-blue tanzanite, a rare gemstone found only in the shadow of Mount Kilimanjaro.
Cellphones link people in the developing world in ways no one imagined just a few years ago. In South America, the cellphone has become a tool of rebellion, and a de rigueur accessory for crime bosses who, in certain corners of the region, act as a kind of parallel government.
In Brazil, drug kingpin Luiz Fernando da Costa was widely believed to have used a cellphone from his prison cell to control his minions in the ''favelas," or slums, of Rio de Janeiro, leading authorities to install jamming devices outside the city's largest penitentiaries.
In China, which has more than 300 million users, the cellphone has come to symbolize the national search for prosperity and self-expression.
On the streets of Beijing, along with on-the-go businessmen, farmers chatter on cellphones as they drive their vegetables to market in mule-drawn carriages.