Don't overlook the underbanked: there are some 35 million of them.

That's the central message of a Javelin Strategy and Research report released Thursday that describes the market for underbanked consumers — 15% of the adult population — and offers strategies for turning them into fully banked customers.

By underbanked, Javelin is referring to those who don't have a checking account or a primary banking relationship. They may have a prepaid card. (The unbanked have no bank relationship at all.) They tend to be young — 36% are 18 to 24 years old.

Their youth means "a big portion of this group will change; they're not going to be underbanked in the future," says Mary Monahan, executive vice president and research director for mobile at Javelin, who spoke Wednesday with Bank Technology News.

"What's interesting about this population is their income is not as low as you'd expect," Monahan says. The average income of the underbanked among the 3,001 consumers with mobile phones surveyed in June 2011 was $52,000; the average among all those surveyed was $73,000. The underbanked are slightly more likely to be black or Latino than white.

The underbanked is not one group of people, but rather several different groups, Monahan notes. One group is the unemployed. Although the national unemployment rate is only 8%, that number doesn't include people who have been out of work for a long time, so the true percentage of unemployed is much higher. Among the underbanked, the unemployment rate is 12%. "Being unemployed hurts people's credit, and sometimes they can't get a checking account," Monahan observes.

Another group is the tech-advanced underbanked, who make heavy use of smartphones and use their smartphones as computers, watching TV and paying bills with them.

There's a tech-challenged group that uses prepaid phones or phones with no data plans. These consumers will need simple SMS banking and alerts.

Another category of underbanked is the immigrant who needs to send money to people in his home country. This group tends to use a lot of wire transfers and remittances. More than twice as many underbanked consumers send wire transfers as all consumers, and three times as many use remittance services. But even more say they would likely use mobile international P2P, even though it doesn't yet exist.

"Remittances are expensive because they're cash-based," Monahan says. "If you can turn that into mobile transactions, that lowers expenses but also creates opportunities for other companies to serve this population. Once they're able to do things like take pictures of checks to deposit them, they don't have to turn them into cash, they can transact using person-to-person payments and prepaid accounts. That really opens the door to turning a cash-based economy to a digital economy."

This can help the countries receiving the money, she says, because "now something that wasn't showing up in GDP is showing up. It's good for institutions because they can get a sliver of these transactions, and it's cheaper, better and safer for the consumer. They don't have to carry cash and they don't have to walk over to the drugstore to cash a check."

The underbanked typically have less access to desktop computers (60% vs. 72% for all consumers) and are less likely to pay for broadband services (34% vs. 59%). "If you try to make them use online banking, you're cutting off your nose to spite your face because they're not going to do it," Monahan says. "You want to allow them to transact via mobile. They're already showing a higher propensity to do mobile banking."

What are these people using instead of using banks? Mostly they just use cash. About 8% use prepaid cards. "These are people who don't have other habits, you're not displacing anything," Monahan says. "It's real easy to supply something that works better."