Millennials dominate mobile banking, according to a Nielsen study Telmetrics released this week, the xAd/Telmetrics U.S. Mobile Path-to-Purchase Study. (Millennials are people born from the early 1980s to the early 2000s.) The report shows that nearly half of all mobile banking users are under the age of 35, and one-third indicated that smartphones were the most important device for their banking needs.

Nielsen surveyed 2,000 smartphone and tablet users in the U.S. about their "path-to-purchase" behavior on mobile devices, as it did last year. This year for the first time, the company gathered information about consumers' use of mobile and online banking.

What does "path to purchase" mean in the context of banking?

"We're talking about the end transactions," says Bill Dinan, president of Telmetrics. "It could be someone paying a bill; applying for a new credit card, a line of credit, or a loan; or looking for investment services. The path to purchase is the conclusion of a transaction."

Nearly 50% of online banking occurs on smartphones and tablets and 54% of mobile banking users complete banking transactions on their mobile device, the report found.

The impetus for the study was the fact that while everyone knows smart phones are being used extensively, mobile advertising dollars aren't necessarily following. The research was meant to show how the extent to which consumers use mobile devices for purchases and banking transactions, and therefore banking sites and apps could be a strong vehicle for ads.

"Some people will tell you the mobile browser is dead and apps are taking over. That's not the case," Dinan says. "It's a world where people are on smart phones and tablets, and usage is different for somebody whether they're at home or on the road. The form factor is different as well." However, conversions are high across all devices, Dinan says.

The study found that nearly three out of four younger users of mobile banking notice mobile ads as they bank. Millennials are partial to coupons and special offers, he says. "For the millennial group it was all about the discount, the coupon, half a point off the interest rate."

For the next age group, those 45 and older, a targeted, relevant ad is important.

All of this means banks could eventually seek revenue from search-related ads the way Google does, Dinan suggests. They could marry basic customer information to incoming transactions to offer up real-time ads and offers, he believes (and some banks already do this, of course). "They should know the age group I'm in; there's demographic information available that can help say, this guy is coming in and applying for a loan, so he might be looking to buy a car or buy a home. What kind of ad can I serve up now for that person?"