Walmart has announced the expansion of its iPhone "Scan & Go" self-checkout program to more stores in the United States as part of an ongoing test.

Reuters reports the number of stores supporting "Scan & Go" will reach 200, up from 70 stores. It is an interesting concept from the nation's most-known retailer, allowing shoppers to scan bar codes on items they want to buy. Once a shopper is ready for checkout, there is a special self-checkout area that connects with the app and prompts the shopper to pay. 

The "Scan & Go" platform lets customers bypass registers, which can become a hassle in busy Walmarts. Another benefit is the ability to keep track of purchases and a running total before going to check out. Walmart's Gibu Thomas told Reuters that more than half of the customers who've tried "Scan & Go" have used it a second time. 

While limited to iPhone right now through the official Walmart app, the platform will launch on Android soon, the company said. Walmart has also hinted at the possibility of digital coupons. 

Of the 200 stores in the programme, it is still a small fraction of the 4,000 Walmart locations in the US. Denver, Phoenix, Nebraska, Texas, Oklahoma, Wyoming, Montana, Seattle and Oregon are among the markets.

Walmart's self-checkout is still not as easy as Apple's EasyPay. The service lets Apple customers go into a store, scan the item themselves, pay through the Apple Store app, and walk out.