Technologies already exist that could allow mobile phones to function as payment devices. Near-field wireless chips can pass information to reading devices at distances of up to a few centimeters. In fact, consumers in Japan and Korea already use phones containing such chips to pay for public transit, buy snacks from vending machines, and check in to flights.

These chips are expected to appear in growing numbers of smart phones, but clever apps are needed to make payment services more attractive. For mobile payment systems to really take off, says Christina Nguyen White, a user experience designer at ­SapientNitro, applications will have to do more than just replace the cash part of the transaction; they’ll need to incorporate the functions of other things people carry in their wallets, such as ID cards and store loyalty cards. “A digital wallet is literally taking that fat wallet out of your purse or your pocket and sticking it in a digital device,” White says.

In one effort in the United States, ­PayPal—best known for providing online person-to-person payment—has entered into a partnership that lets its payment processing system link up with the mobile payment system offered by the startup Bling Nation. Users receive stickers containing a near-field communication chip, which they can slap on their phones to start making payments through a PayPal account. Bling Nation has signed up a variety of local retailers across the country, including coffee shops, restaurants, and gas stations.

Even if people choose to hang on to their credit cards, they still might end up paying by mobile phone at businesses that use Square, a service that brokers card payments from Apple and Android mobile devices. Sellers plug a small card-swipe magnetic reader into the device and use a downloaded app to process payments, sending Square a commission on each transaction.