On a planet of nearly 7 billion people, 5 billion use mobile phones -- and of those mobile phone subscribers about 70 percent are in emerging economies, according to U.N. estimates.
It's no wonder health organizations are looking to the massive medium as a means to inform the public on health news, and in particular help populations that don't have easy access to medical treatment.
The use of mobile phones for medical purposes, known as mHealth, has been around for a decade and new projects are launching all the time.
For example, pregnant women in countries such as India and South Africa who can't visit doctors regularly now can register their due dates and receive SMS -- or text -- messages with information that matches up with their babies' development, such as what food they should be eating.
In Bangladesh, parents can receive alerts telling them when to bring their children into clinics for vaccinations.
In the United States, Health and Human Services Secretary Kathleen Sebelius recently announced a new initiative to text-message tips and health information to motivate people to quit smoking.
But despite the promising implications for health, there are still some challenges to overcome -- as those involved in the effort can attest.
"The challenge is people have cell phones, but so many components come into play" from people heeding the text messages to making sure the messages have value for them, said Patty Mechael, executive director of the U.N. Foundation's mHealth Alliance. "What's relevant for Bangladesh might not be for Africa or Brazil."
For a long time, she said, research focused on the computer science side and whether the user liked it, not whether users were getting healthy results. What's missing is evidence around what works and what doesn't, she added.
So organizations are investing in more and more in research to understand the behaviors that they are trying to change as well as working out processes to adapt messages to different contexts -- not only from country to country, but within a certain country as well, said Mechael. Those processes involve both cultural and language adaptation, and testing.
In August, the Lancet published an article on a cluster randomized trial that showed text-messaging health care workers in Kenya increased the number of patients who received correct malaria treatments.
But more research is needed, and in order to scale up successful pilot projects, governments will need to be on board.
More questions revolve around whether applications can be used across all mobile devices, and how to charge cell phones in areas where electricity is spotty or nonexistent.
Josh Nesbit, CEO of Medic Mobile, a nonprofit based in San Francisco, said in the absence of readily available electricity, there are some alternative fixes. A device used in Tanzania and some other countries allows bicyclists to charge their phones while they ride. Also, small, individualized solar panels can be purchased for little money and shared in the community to charge phones.
On the big question of whether people will actually use the text-messages, Nesbit said studies are underway. His company maps out a behavior chain gauging people's access to phones and cell towers, and what incentives are in place for people to use them, such as credits and other payments.
But when it comes down to it, the system has to deliver for the user to be motivated to use it, he said.
Despite all of the challenges, there is progress, especially in the area of collecting health information. "Health is very data-driven, so a lot of the decisions being made within programs rely heavily on the data that's being collected" on PDAs -- or palmtop computers -- and now with smart phones, said Mechael. Instead of taking a year to collect the information, it arrives much faster by phone and can keep pace with changing medical needs, she said.