T-Mobile (TMUS) has been shaking up the phone industry under CEO John Legere. Now it’s taking aim at banking as well.

On Wednesday the carrier is opening a new financial services program, called Mobile Money, aimed at customers who don’t have a regular bank account and depend on high-fee alternatives such as check cashers and payday lenders.

All of Legere’s previous efforts were aimed at lowering the cost of mobile phone service. But the company’s research discovered many customers also struggled with overpriced and inconvenient payment options for all of their bills.

“That was something we weren’t necessarily looking for,” says Taylor Collyer, a senior director at T-Mobile who worked on the Mobile Money project. But since the company already collected monthly fees and offered installment plans for phones, “we do finance – we know a fair amount about that,” Collyer adds.

Signing up

To start, customers will have to sign up for Mobile Money at one of T-Mobile’s 3,000 retail locations. They can add money to their account by handing cash to a store clerk, signing up for direct deposit or using a mobile app to snap a picture of a check. Funds added via direct deposit, which can be done with paychecks and government benefits checks, will be available two days early.

Money added to an account will be available by way of a Visa (V) debit card, which can be used at any store that accepts Visa and across a large ATM network. The mobile app, available for Google’s (GOOG) Android and Apple’s (AAPL) iOS, will also have online bill-paying capability. Additionally, the app can be used to transfer money directly to another Mobile Money user.

At least initially, Mobile Money users won’t be able to pay for things with their phone – they'll have to use the Visa debit card. But T-Mobile says it's looking at adding Isis, a tap-to-pay service run by credit card and mobile phone companies, to Mobile Money later on.

T-Mobile customers who sign up for the new service won’t pay any fees, including for accessing ATMs. People who are not T-Mobile phone customers will have to pay a $5 per month maintenance charge and some other fees.

Numerous studies have found that about 70 million Americans don’t have ready access to banking services. The reasons are complex and include language barriers, a smaller number of banks in low-income neighborhoods and lack of education about financial services. People who don’t use banks end up spending a significant portion of their income – about 6% for a household that makes $20,000 a year – for alternatives, according to a study by the St. Louis Federal Reserve.

T-Mobile is not the first company to attack the problem. Wal-Mart (WMT) teamed up with American Express (AXP) in 2012 to create a similar service called Bluebird, for example. Over 1 million people have signed up and added over $1 billion, American Express said in August.

But T-Mobile may have an advantage since so many low-income people already have mobile phones, and the carrier has numerous stores in inner cities and other places where banks are scarce. Mobile phone carriers have created popular banking products in other parts of the world. Almost 20 million people use Kenya’s M-Pesa mobile banking program.

Legere and his team have shown a knack for identifying things that annoy consumers and creating appealing solutions. T-Mobile brought in 4.4 million new customers last year, after shedding customers in 2012, and the company’s stock price has doubled since debuting on the New York Stock Exchange in May.

T-Mobile has been piloting Mobile Money in the Miami area over the past few months and usage exceeded expectations, Collyer says. Many customers used it as a primary bank account, but others used it in more creative ways, such as for paying a child’s monthly allowance.

“We’re very confident that we have the value proposition correct for the customer,” Collyer says.

If he’s correct, T-Mobile may be spreading its disruptive ways to a whole new market.