Watching his sons kick around a makeshift ball made from tightly bound plastic bags, Ugandan handyman Jackson Mawa marvels at the way business has improved since he bought a solar-powered mobile phone.
"I am self-employed. Sometimes people call me and they find my (cell) phone is off. I have been having that problem a lot due to battery charging. So when (Uganda Telecom) brought out the solar phones, since I got it, that very day, I have never had any problem with my phone," said Mawa, clutching the device.
It might not sound like much but for Mawa and millions of people in Africa and Asia, with no connection to electricity grids or unreliable and expensive power access, these little solar-powered gadgets are proving to be revolutionary.
Farmers can check market prices before deciding which crop seeds to sow, speak to buyers from their fields and get weather forecasts. And unlike with standard mobile phones, they don't have to worry about their phone battery losing power.
Solar cell phones could build on the economic advantages that mobile phones have already brought to far-flung regions of Africa and the Indian subcontinent, including price transparency and more accurate and timely information.
Mobile phone penetration in these regions has been held back by a lack of electricity: there is simply no way to charge a cell phone in many rural areas of developing countries.
An estimated 1.6 billion people have no access to electricity at all, while another 1 billion people have no electricity for much of the day, according to estimates by development groups.
Fortuitously, perhaps, most of these people live in sunny climates. And this is where solar mobile phones come in.
"If you look at the map of countries with low tele-density — there is plenty of sunshine everywhere," says Rajiv Mehrotra, chairman of VNL, a company making solar-powered mobile network base stations in India.
Take Uganda as a case in point: Just eight percent of the country's 32 million plus population have electric grid access. Even when the grid is there, like where Mawa lives in Mulago, a poor suburb of Kampala, the power is costly and the service is intermittent.
"In our area, electricity is expensive so at six o'clock in the morning, we turn our power off until six in the evening," said Mawa, 29, sitting on a step outside his house.
Until solar cell phones were introduced, charging a phone in remote areas, off the electricity grid, entailed a bone-jarring journey to the nearest town, where the phone battery could be charged at kiosks run on generators for relatively hefty fees.
The journey might take all day and the battery charge fee might cost more than that day's lost wages.
There are more than 3 billion people using mobile phones around the world and most of the next billion users will come from emerging markets, particularly in the countrysides of these markets.
"There is a significant opportunity within developing markets where there is limited access to grid electricity," said Windsor Holden, principal analyst at telecoms research firm Juniper Research.
The makers of solar cell phones such as Nokia, Samsung and ZTE see the rural poor in these emerging markets as their main customer base rather than carbon-conscious consumers in the West.
"People's need to communicate is so high. It's running miles ahead of the power grids expansions," says Anne Larilahti, head of environmentally sustainable business at network equipment maker Nokia Siemens Networks.
Across the ocean, in India's remote Orissa state, farmers living off the power grid are generating electricity with solar power which is making inroads in rural India and Bangladesh. For them, solar-powered cell phones are a natural extension.
The potential in rural India for cell phone makers and operators is huge. Consider this: India had nearly 500 million wireless users, and some 10 million new users are signing up each month. That doesn't count the millions in India's remote villages where electricity is rare or non-existent.
Tapping this new market as well as earning green points, is attracting mobile phone companies such as South Korea's Samsung which released its first solar-powered phone model, Solar Guru, in India in June.
"We contact doctors for health related advice. We seek information on weather from local official. We speak to local agriculture officials and discuss with them problem related to crops," said Indian farmer Jhasketan Pradhan.
Solar phones are not new: The top phone maker Nokia sold a model a dozen years ago, but with technology development their usability and prices are starting to reach masses.
About an hour of solar charging offers around 5-10 minutes of talk time. Selling at around $60, Samsung Solar Guru features FM radio, MP3 ring tones, embedded games, and a torch light.
If demand for such phones really takes off, it is a risk for Nokia, who likely cannot watch for long from aside as its market share in India and in Africa is 60-70 percent.
With proper positioning and pricing, solar-powered cell phones could reach about two billion people across the globe who have no access to electricity. Aside from the commercial opportunities, there are very real economic benefits.
"Nowadays, farmers use mobile phones to know about the market situation ... so that the middlemen cannot exploit them and this is happening in Bangladesh, this is happening in Uganda, this is also happening in India," said Abdul Bayes, an economics professor from Bangladesh's Jahangirnagar University.
Bayes, who has studied the impact of mobile phones on developing economies, estimates that GDP increases by one or two percent for every 10 percent increase in mobile phone access.
Savings, he said, come not just with improved market knowledge but by increasing productivity as farmers can call for information rather than leave their fields to travel to the city to speak to buyers and suppliers.
A major appeal of solar-powered cell phones is the growing consumer demand for environmentally sustainable mobile phone devices, and annual sales of greener phones could grow to 105 million handsets by 2014, said Holden, of Juniper Research.
The world's largest consumer electronics sector by volume, the cell phone industry is keen to tap consumers' increasing interest in more environmentally friendly phones.
The sector is closely followed by environmental organizations due to its large scale. More than 1 billion phones are sold globally each year, which requires the use of sales boxes, add-ons and tonnes of raw materials including rare metals.
Solar phones still have a long way to go in terms of offering sophisticated features already existing in conventional handsets, and some doubt if it's green features help reduce carbon emissions in a significant way.
"If you think about it, mobile handsets on the grid uses comparatively little electricity and chargers are becoming increasingly efficient in the amount of power they use," said Holden.
An average mobile user is responsible for around 25 kg of C02 emissions per year, said Holden, a collective total of 93 megatonnes of CO2 globally as of the end of 2008. Electricity consumed by charging mobile phones contributes to just a fraction of such emissions.
Sony Ericsson and Nokia are rolling out phones with greener features such as lower energy consumption, use of recycled materials, smaller packages and electronic user manuals. Meanwhile, Samsung and ZTE are pushing ahead with solar phones and Sharp is releasing its own model in Japan this year. It's not clear what Nokia's plans are in the solar phone department as it keeps a tight lid on its future product lines.
In Africa, Kenya's Safaricom has already sold out its first batch of solar-powered mobile phones made by ZTE since the phones were launched in August.
"It's selling pretty good because if we compare with other phones that (are also new to the market), they were not doing as well as we are having this one do," said Gladwell Mbugua, a Safaricom sales agent in Nairobi.
Michael Joseph, Safaricom's chief executive, said the phone was popular in rural areas where there might be no electricity, but also with young people who are always on the move like his 20-year-old daughter and her friends.
"From coffee to lunch to parties, they don't have time to charge their phones," Joseph said.