"The phone rang and I heard Isatu's cheery voice," said Moiyattu Banya, who co-founded the Girls Empowerment Summit Sierra Leone two years ago. "She was flashing me."
Isatu is one of the girls, aged 12-16, who have participated in the annual Empowerment Summit in Sierra Leone's capital and in the regular gatherings organized between summits. During the Ebola crisis, all those sessions have been suspended, and Isatu was eager for a mentor's encouragement over the telephone.
Many people across Africa, as well as in other regions, use the tactic of phoning someone and hanging up, hoping the party contacted will ring back. As in the case of Isatu's flashing, the caller might also send a quick SMS or voice message. "Aunty Moiyattu," appealed Isatu hastily. "Call me back - I don't have any credits."
The practice of flashing - also called 'beeping', and in French-speaking areas, 'bipage'- arose from widespread mobile phone pricing in much of the developing world, where service providers bill only the originating party for air time. The recipient of a phone call isn't charged, even if the conversation is lengthy.
The very term 'flashing' can confuse mobile phone customers in the United States and other wealthy countries, where it refers to reprogramming cellular phones to transfer from one provider to another. In addition, U.S. usage plans typically are for annual packages that are billed monthly. Both the caller and the called are charged for the air time used. That's a good deal for phone companies - not so much for phone users, especially in poorer countries.
Phone-charging patterns across Africa gave rise to a variation on phone tag, which is designed not to reach someone but to avoid connecting. Friends often develop complex signals - one ring, for example, or two, to convey such messages as 'meet me' or 'don't forget' or 'I'm OK'.
Several phone companies, in an attempt to make some money from the millions of 'missed' calls, developed free or low-cost messaging systems allowing users to send a message like 'call me back', which are then routed to the recipient using a cheaper technology than that for phone calls.
Health services have begun making use of beeping in resource-poor settings. A pilot programme in Swaziland, where over two-thirds of people have mobile phones but where text messages are too costly for most of them, used missed calls, dubbed 'buzzing', to remind HIV patients to keep follow-up appointments.
Described in the journal Infectious Diseases and Poverty last year, more research is needed to measure whether health outcomes improve, but the experiment had a 100% uptake from patients and positive reviews from both patients and health-care workers.
Even before Ebola hit, Sierra Leone was among the poorest countries in the world, with one of the highest rates of infant deaths as well as of maternal mortality - the number of women who die from pregnancy and childbirth. But the country was making substantial progress, for example, lowering maternal deaths from 2200 per 100,000 live births in the year 2000 to 1100 per 100,000 live births in 2013.
The shock of Ebola has stalled those advances and threatens to reverse them. The creative use of mobile phones has become a weapon in the response.
Banya, a feminist writer with a graduate degree in Social Enterprise and Non Profit Management from Columbia University in New York, quickly returned Isatu's call.
"Knowing that the girls relied on our support and on each other for support,", Banya said, "our staff devised a plan to call them every two weeks to ensure that everyone was doing well and to take note of any emerging needs with which we could assist."
For a city like Freetown, cell phones have become a lifeline in more ways than communicating with trusted mentors. The government of Sierra Leone has partnered with cell-phone company Airtel and the International Federation of the Red Cross and Red Crescent Societies (IFRC) to send some two million text messages monthly about Ebola since April.
Messages include telling people not to fear health workers in protective suits. Unlike many text message initiatives, this one allows recipients to reply with questions. And it can be geo-targeted to customize information for a particular area.
This is not the first time that cell phones have helped Freetown face a health crisis. The capital city sprawls up hillsides from a busy harbor and port. Over a million of the country's six million population live in the city, which grew more and more crowded as people fled civil war in the countryside over the ten years that ended in 2002.
The city's low-lying areas are increasingly prone to flooding from rising sea levels and the fierce storms that accompany climate change.
In 2012, impoverished neighborhoods like Kroo Bay - where the average life span of its 6000 residents is only 35 years - were awash in cholera, as well as in torrential rains that spread the disease. The government declared a state of emergency. To combat the spread of infection, Airtel flooded its customers with messages about hand washing and sanitation.
The IFRC says it plans to expand the new SMS service to seven countries in the region, providing it can get cooperation from network providers and government officials. Once in place, the system can be used to warn urban residents of current hazards of all kinds and direct them to assistance.
This year's floods in Freetown, which are worst during the rainy season months of June, July and August, complicated the process of accessing treatment for Ebola victims. The IFRC project's ability to alert people to impassible areas and direct them to the nearest health facilities - for Ebola and non-Ebola illnesses alike - may have helped to save lives.
Phones can also inform and remind girls of school lessons on the radio - an attempt to mitigate the effect of the government order that shut schools to minimize the spread of Ebola.
"Any stretch of time that the girls spend out of school is detrimental to their learning and social functioning," Banya wrote on the website of the African Womens Development Fund (AWDF), which has made numerous grants supporting Ebola-affected areas. Banya wrote that the school closure "severely impacts children in the country, especially girls, who are already at a disadvantage when it comes to secondary education."
Women and girls are critical for addressing Ebola and for raising communities generally, said AWDF CEO Theo Sowa. "Women are the ones who have primary responsibility in most of our communities for family and family responses. If we look at the HIV/AIDS crisis, if it hadn't been for African women, our continent probably wouldn't have survived," she said. "It was women who were the caregivers, women who worked to help change behaviors, women who took care of treatment. Women have trusted relationships with their families and communities. If we want to crack any problem on our continent, women have to be at the heart of the response."
The Girls Empowerment sessions in Freetown aim to prepare vulnerable girls for playing leadership roles in their neighborhood and in the country. But like school classes, those, too, had to be postponed due to Ebola. Telling Isatu that "was one of the hardest conversations I have had this year," said Banya. She encourages the Summit girls to keep writing in their journals and to keep in touch by phone.
"I can only hope," she said, "that all they have learnt in these two years will keep them connected and keep them going through these hard times."
Reporting on African cities and their efforts to build resilience is supported by the Rockefeller Foundation.