YANGUYE, South Africa - On this dry mountaintop, 36-year-old Bekowe Skhakhane does even the simplest tasks the hard way.
Fetching water from the river takes four hours a day. To cook, she gathers sticks and musters a fire. Light comes from candles.
But when Ms. Skhakhane wants to talk to her husband, who works in a steel factory 250 miles away in Johannesburg, she does what many in more developed regions do: she takes out her mobile phone.
People like Ms. Skhakhane have made Africa the world's fastest-growing cellphone market. From 1999 through 2004, the number of mobile subscribers in Africa jumped to 76.8 million, from 7.5 million, an average annual increase of 58 percent. South Africa, the continent's richest nation, accounted for one-fifth of that growth.
Asia, the next fastest-expanding market, grew by an annual average of just 34 percent in that period.
"It is a necessity," said Ms. Skhakhane, pausing from washing laundry in a plastic bucket on the dirt ground to fish her blue Nokia out of the pocket of her flowered apron. "Buying air time is part of my regular grocery list."
She spends the equivalent of $1.90 a month for five minutes of telephone time.
Africa's cellphone boom has taken the industry by surprise. Africans have never been rabid telephone users; even Mongolians have twice as many land lines per person. And with most Africans living on $2 a day or less, they were supposed to be too poor to justify corporate investments in cellular networks far outside the more prosperous cities and towns.
But when African nations began to privatize their telephone monopolies in the mid-1990's, and fiercely competitive operators began to sell air time in smaller, cheaper units, cellphone use exploded.
Used handsets are available for $50 or less in South Africa, an amount even Ms. Skhakhane's husband was able to finance with the little he saves from his factory job.
It turned out that Africans had never been big phone users because nobody had given them the chance.
One in 11 Africans is now a mobile subscriber.
Demand for air time was so strong in Nigeria that from late 2002 to early 2003 operators there were forced to suspend the sale of subscriber identity module cards, or SIM cards, which activate handsets, while they strengthened their networks.
Villagers in the two jungle provinces of Congo are so eager for service that they have built 50-foot-high treehouses to catch signals from distant cellphone towers.
"One man uses it as a public pay phone," said Gilbert Nkuli, deputy managing director of Congo operations for Vodacom Group, one of Africa's biggest mobile operators. Those who want to climb to his platform and use his phone pay him for the privilege.
On a continent where some remote villages still communicate by beating drums, cellphones are a technological revolution akin to television in the 1940's in the United States.
Africa has an average of just one land line for every 33 people, but cellphones are enabling millions of people to skip a technological generation and bound straight from letter-writing to instant messaging.
Although only about 60 percent of Africans are within reach of a signal, the lowest level of penetration in the world, the technology is for many a social and economic godsend.
One pilot program allows about 100 farmers in South Africa's northeast to learn the prevailing prices for produce in major markets, crucial information in negotiations with middlemen.
Health-care workers in the rural southeast summon ambulances to distant clinics via cellphone.
One woman living on the Congo River, unable even to write her last name, tells customers to call her cellphone if they want to buy the fresh fish she sells.
"She doesn't have electricity, she can't put the fish in the freezer," said Mr. Nkuli of Vodacom. "So she keeps them in the river," tethered live on a string, until a call comes in. Then she retrieves them and readies them for sale.
William Pedro, 51, who deals in farm and garden plants, said he tried for eight years to lure customers to his nursery in a ragtag township near George, a resort town on South Africa's southern coast. Only when he got a cellphone two years ago, he said, did his business take off.
"White people are afraid to come here to my place in the township to buy plants," Mr. Pedro, who is of mixed race, said as he stood outside his makeshift greenhouses. "So now they can phone me for orders and I can deliver them the same day."
Hamadoun Touré, development director for the International Telecommunication Union, said the economic blessings of cellphones were magnified in the developing world.