SHANGHAI—Wu Jun’s rose gold iPhone is a financial supermarket.

The 33-year-old market researcher in Shanghai usually keeps yuan equivalent to a few hundred dollars deposited online to cover her daily spending—and more ahead of big sales. It takes her only a few taps on the screen to buy investment funds, split restaurant bills with friends and send cash to family members. She recently dipped into the account for a $7.50 box of tea at a Shanghai convenience store.

...