KHAYELITSHA TOWNSHIP, South Africa—Mavis Nonkongozelo walks up to the Five Sisters convenience store here, then pulls a mobile phone from her bag and a few rands from her brassiere. She is ready to bank.

With a few taps on her cellphone, the 34-year old preschool teacher connects to a nascent mobile-banking network aimed at Africa’s new consumers. The saleswoman accepts a 20 rand ($2.94) bill through a barred window and then taps back on her cellphone. Soon, the money is credited to a special no-fee account at Standard Bank, South Africa’s largest.

From this corrugated-metal shack outside Cape Town, Standard is breaking from its main business of drawing customers to its branches and automatic teller machines in favor of a low-cost mobile-phone model that is based on proximity to people, like Ms. Nonkongozelo, who have never banked before. The shift says a lot about where banks are placing bets on Africa’s economic growth as a new middle class emerges.

Since an official launch last year, Standard has opened more than 8,300 of these so-called “bank shops” at sites ranging from street-side convenience stores to raucous taverns. By the end of this year, Standard intends to have 10,000 set up around the country, mostly in South Africa’s predominantly black townships, and has recruited local sales agents to find customers. The shops aim to tap what executives estimate is a pool of about 15 million people in South Africa, or about 30% of its population, who don’t have active bank accounts but now have the means to spend and save.

Standard doesn’t charge for this type of account, but the bank earns small commissions on cash transfers and those who stock up on mobile-phone credit. “It’s not a golden pot of money,” says Thoraya Pandy, one of the managers at Standard spearheading the mobile-banking program. “We need to bring in loads and loads of customers.”

Follow this link to read more: