Earlier this month, on a short bus ride through the centre of Kampala, I decided to carry out an informal survey. Passing through the Ugandan capital's colourful and chaotic streets, I would attempt to count the signs of the use of mobile phones in evidence around me. These included phone shops and kiosks, street-corner airtime vendors and giant billboard ads, as well as people actually using their mobile phones: a girl in school uniform writing a text message as she hurried along the street, a businessman calmly making a call from the back of a motorcycle taxi swerving through heavy rush-hour traffic. Not only were half of the passengers on my bus occupied with their handsets, our driver was too, thumbing at his keypad as he ferried us to our final destination. After five minutes, I lost count and retired with a sore neck. There was more evidence here than I could put a number on.

My survey underlined a simple fact: Africa has experienced an incredible boom in mobile phone use over the past decade. In 1998, there were fewer than four million mobiles on the continent. Today, there are more than 500 million. In Uganda alone, 10 million people, or about 30% of the population, own a mobile phone, and that number is growing rapidly every year. For Ugandans, these ubiquitous devices are more than just a handy way of communicating on the fly: they are a way of life.

It may seem unlikely, given its track record in technological development, but Africa is at the centre of a mobile revolution. In the west, we have been adapting mobile phones to be more like our computers: the smartphone could be described as a PC for your pocket. In Africa, where a billion people use only 4% of the world's electricity, many cannot afford to charge a computer, let alone buy one. This has led phone users and developers to be more resourceful, and African mobiles are being used to do things that the developed world is only now beginning to pick up on.

The most dramatic example of this is mobile banking. Four years ago, in neighbouring Kenya, the mobile network Safaricom introduced a service called M-Pesa which allows users to store money on their mobiles. If you want to pay a utilities bill or send money to a friend, you simply dispatch the amount by text and the recipient converts it into cash at their local M-Pesa office. It is cheap, easy to use and, for millions of Africans unable to access a bank account or afford the hefty charges of using one, nothing short of revolutionary.

Safaricom didn't invent mobile banking: it existed previously in countries such as Norway and Japan, but on a small scale and with nothing like the seismic effect it had in Kenya. The established banks weren't happy at first – they tried to shut down M-Pesa soon after it started – but now they are getting in on the game, and it is estimated that by 2015 global mobile transactions will exceed one trillion dollars. According to California-based mobile-banking innovator Carol Realini, executive chairman of Obopay: "Africa is the Silicon Valley of banking. The future of banking is being defined here… It's going to change the world."

Watch Yousef Eldin's video exploring the impact that new developments in mobile phone technology are having on life in some of Uganda's most isolated communities guardian.co.uk

The mobile banking phenomenon spread quickly to other countries in the developing world. Uganda's largest telecom company, MTN Uganda, created its own version, MobileMoney, in March 2009. Within a year, 600,000 Ugandans had signed up. Now, thanks to aggressive recruitment drives to win more subscribers – MTN agents trolling the streets for new customers are known as "foot soldiers" – the service has more than 1.6 million users.

MobileMoney outlets are everywhere in 2011: the distinctive canary-yellow buildings and kiosks that house them are dotted around not just Kampala but the greater part of the country. The MTN network reaches 85% of Uganda, and MobileMoney is available everywhere MTN has coverage. Many of the villages I travelled through, however minor or remote, had at least one tell-tale splash of yellow.

Mobile phones carry huge economic potential in undeveloped parts of Africa. A 2005 London Business School study found that for every additional 10 mobile phones per 100 people in a developing country, GDP rises by 0.5%. As well as enabling communication and the movement of money, mobile networks can also be used to spread vital information about farming and healthcare to isolated rural areas vulnerable to the effects of drought and disease.

Despite the proliferation of phones in Uganda, however, a digital divide persists. How can information be understood and properly implemented when more than a third of the country's adult population cannot read or write? And can complex and detailed information be managed by anything less than a smartphone, which is beyond the means of most Ugandans?

One intriguing solution to these problems is being tried out by the microfinance organisation Grameen Foundation. Seeking to establish a reliable means of interacting with farming communities in the Ugandan countryside, Grameen has started to lease smartphones to local farmers so that they can receive information – seasonal weather reports, planting advice, disease diagnostics, market prices – and pass it on to their neighbours. They also gather information from the farmers they register and feed it back to Grameen in Kampala, which passes it on to agricultural organisations and food programmes.

These intermediaries, known as community knowledge workers (or CKWs), are chosen for their command of English, community standing and entrepreneurial spirit as well as their technological know-how. After training CKWs to use smartphones, Grameen pays them a performance-based wage averaging at about $20 per month – via MobileMoney, obviously. Deductions are made to cover the lease arrangement and high-performing farmers can expect to fully own their phone, and the charging solution that comes with it, within two years.

So far, Grameen has trained 500 CKWs in 32 Ugandan districts, reaching more than 20,000 households, or 100,000 people. "We're aiming for a million," says Sean Krepp, Grameen's Uganda director, "and we're looking at scaling this to several other countries."

Before that can properly happen, the technological side of the programme needs to be developed and refined. At present, most information arrives in text form. Reports from a variety of sources, including Uganda's Department of Meteorology and its National Agricultural Advisory Services, are rewritten in clear English before being dispatched to the CKWs. Grameen has started sending images to its representatives so that, for example, a coffee plant disease can be diagnosed by visual means. The next step, according to Krepp, is video. The economist Philip Parker, in collaboration with Grameen, is currently developing a series of educational videos, presented in the style of a gameshow, to be played on CKW smartphones during village get-togethers.

There are other, more fundamental challenges. Unreliable network coverage in remote areas of Uganda is a significant problem. Keeping smartphones charged in villages that don't have electricity is another. Some ingenious solutions have been devised (see below), but low battery power remains a constant headache.

In spite of these obstacles, the programme appears to be working – and its potential for expansion, not just beyond Uganda's borders, but also into other areas, such as healthcare and education, is becoming clear. If the digital divide is being bridged in some of Africa's poorest communities, and the information is getting through, why stop at farming?

Case study 1: a mobile money micro-economy

Boat owner Allan Mukasa uses his phone to settle bills and pay local traders. Photograph: Yousef Eldin

Kasensero: Rakai district

The small fishing village of Kasensero on the shores of Lake Victoria is a 200km drive from Kampala, heading south-west towards the border with Tanzania. The final 40km takes you down a bumpy red-clay road, which on rainy days becomes a muddy assault course. When you finally reach the village, a road barrier blocks your way until an elderly guard deems you fit to enter and raises it up.

At the end of the main street is Africa's largest lake and the main source of the town's industry. Here, lined up along the shore, are hundreds of long, narrow fishing boats piled high with nets. The morning's catch is in when I arrive in Kasensero and the last of the giant Nile perch are being carted away towards the factory further down the beach, where they will be processed, packed and sent to Kampala for export.

At the end of the row of buildings overlooking the shore is a distinctive yellow facade: one of two MobileMoney agents in this village of 5,000 people. Inside, Ben Nsubuga, a fisherman, is depositing his weekly earnings.

He hands a wad of cash to the woman behind the desk who logs the deposit in a book and gives him a code, which he enters into his phone. A small fee is charged and within a couple of minutes the transaction is complete.

"Before this service came here, I was keeping all my cash with me," he says. There are no banks nearby and in the past whenever Nsubuga travelled to bring money to his family, he feared being robbed on the long road out of Kasensero. "Now I just send the money this way," he says, gesturing with his phone. The money is transferred via text and the person at the far end can cash it in at any MobileMoney agent.

The biggest problem, he says, is the network, which is patchy in these parts and often leaves customers without ready access to their hard-earned cash.

Next in line is Allan Mukasa, a boat owner and the village's vice-chairman. "Somehow, it has made life here better," he says. As well as sending money long-distance, Kasensero residents bank money on their phone and transfer it among themselves, creating a kind of micro-economy in this isolated town. "We also use it to pay water and electricity bills and school fees," Mukasa adds. But he sees plenty of room for improvement. "Before, we didn't know how to bank. Now, we want to have a proper banking system, with the possibility of making interest."

It is only after I leave Kasensero that I learn about its troubled recent history. In the early 1980s, the town was the site of the world's first community-wide Aids epidemic: a fifth of its population had died of the disease by 1986. Nearly a decade later, several thousand bodies from the Rwandan genocide washed up on its shores, carried to the lake down the nearby Kagera river. A mass graveyard a few kilometres away recalls the horror.

Today, the town is putting its traumatic past behind it and, if the queues outside the yellow-fronted offices are any indication, it is prospering. Only now, Kasensero's money doesn't end up under the mattress: it hovers about in the airwaves, to be accessed or dispatched with the touch of a button and a small charge from MTN. Signal permitting, of course.

Case study 2: farming with a smartphone

Farmer Simon Obwoya, foreground, makes notes on crop conditions and checks market prices. Photograph: Yousef Eldin

Lagude: Gulu district

Shortly after I arrive at the small cluster of mud huts that makes up the tiny village of Lagude, in northern Uganda, my host, Simon Obwoya, announces with great regret that he cannot show me his mobile phone: it was taken to Kampala for repairs two weeks ago. Without it, he is unable to access valuable information that makes farming in this difficult, drought-prone terrain more practicable.

Last December, Obwoya, who is 43 and married with eight children, was recruited as a community knowledge worker by the Grameen Foundation and trained to use a smartphone so that, as well as receiving advice about weather, plant and animal health and market prices, and dispersing it around his local area, he could gather information from the farmers he registers and send it back to Grameen.

Of all the districts that the foundation work with in Uganda, Gulu is the most problematic. For 20 years, much of northern Uganda was a war zone. Terrorised by the notorious Lord's Resistance Army, large numbers of people were forced into grim displacement camps. In the last few years, following the expulsion of the LRA in 2005, people have been slowly returning to their homes, and to normality. But two decades of conflict have taken a heavy toll – on community trust and the motivation to work as well as lives and material wealth. A wealth of farming knowledge has been lost, too, and Simon is working hard to restore that and bring it up to date.

Just before sunset, a Grameen representative arrives from Gulu town on a motorbike with Simon's HTC smartphone, fresh from the menders. Simon is delighted and immediately sets about recharging it: no mean feat in a village without electricity. As part of the lease package, Simon received a lithium-ion "intelligent battery" called a ReadySet, designed by American company Fenix International. It also powers an LCD lamp and a radio, but Simon's ReadySet is low on juice so he charges his phone in our van.

The next morning, Simon sets about addressing the ReadySet issue. He connects the battery to a kinetic generator, which he affixes to the rear wheel of his bicycle. Then he gets on his bike, which is held on a stand, and starts pedalling. The village has become accustomed to the spectacle of Simon cycling without moving, often for hours at a time, in an attempt to recharge his ReadySet.

Unfortunately, it doesn't work as well as it should and he often has to top up the battery at the local trading station, which costs money.

Undaunted, Simon takes me on a tour of his fields, where he grows maize, cassava, groundnuts and beans, and the wider area he administers as a CKW. This encompasses five villages, and Simon has registered more than 300 farmers to the programme in the last six months.

To register, a farmer must provide exhaustive details about his farm, household and income, as well as the things he needs most to improve his livelihood. Many in the area still wonder why Grameen isn't providing them with physical aid, but Simon tells me he is working to change that mindset. "Let someone give you knowledge, then you are rich. That's what I say to my farmers."

Is the knowledge he receives from Grameen actually making a difference? Simon nods. "Especially this year. We were warned there was going to be a long drought so many of our farmers took their time before putting down their seeds. That was what happened and our farmers were able to save their seeds."

Simon has also founded a farming collective and now, with Grameen's help, they are bulking their produce and selling it at a good price to the World Food Programme, which will use it for relief work in the region. The CKW programme has had a rocky start in Gulu, and challenges lie ahead, but in the fields that Simon Obwoya monitors with his treasured smartphone, it is beginning to yield tangible results.