That’s one major takeaway from Bill and Melinda Gates’ annual letter outlining the global trends that the billionaire couple is focused on in 2015. The financial lives of the poor are complicated, they write, and the poorest people around the world do not have access to financial services. By 2030, the explosion in digital banking will give the poor more control over their money and help lift them out of poverty.

The key to that transformation will be mobile phones: In 15 years, 2 billion people who don’t have a bank account today will be saving money and making payments with their phones.

And if women — as opposed to only the husbands — have access to phones, Melinda predicts that the economic transformation across countries will be even more remarkable.

“Women talk about if they can get hooked up to the banking services which have become ubiquitous in places like Kenya and Tanzania, they can then save small amounts of money,” she said in a meeting with a handful of reporters on Wednesday. “Saving a dollar a day or two dollars a day could change everything” for women. And their children.

Since launching the Bill and Melinda Gates Foundation in 2000, the foundation has distributed $31.6 billion in grants, mainly for global health projects in some 100 countries. The Gates believe that as more women save money through mobile banking, there will be a positive ripple effect.

More women will be able to save money and control their finances. In turn, they will be able to use savings for things like health services for their families. By 2030, the number of children around the world who die before the age of five will be 1 in 40, compared to 1 in 10 in 1990, according to the Gates Foundation.

With fewer infant deaths, more families will invest more in their children’s education — which, in turn, would stimulate the global economy, according to the Gates Foundation.

Gates spoke about how much information that people in the Western world take for granted that can be revolutionary for people in poorer countries. Seven out of ten people living in sub-Saharan Africa are farmers, she notes. If these families had access to a mobile phone, they could find out how much their crops are going for in the city market before they make the trip in — which would allow them to more effectively price their own crops and increase profits.

“Fifteen years from now, I want to see these farmers with healthier kids, getting more yield off their farms, getting their boys and girls into the education system and persisting through secondary school,” she said. “That is transformative in their lives.”

Yet the Gates’ acknowledge in their letter that there are cultural challenges that make it difficult for women in many countries to gain access to mobile phones without their husbands’ consent. In Bangladesh, for example, only 46% of women own a phone, compared with 76% of men.

Getting men to think more about the economic benefits of giving their wife access to mobile banking and sending their daughters to school through secondary education is challenging, says Gates. But by rooting the discussion in what is important them, mainly the health of their children, men are more likely to see the benefits of empowering the women in their family to succeed.

“Men and boys have to be a part of it,” she said “They are often the ones making the decisions about [what to do] with very little resources in their family and who they are going to educate.”

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