The company has crushed all competitors through its mastery of supply-chain logistics and inventory management, which above all are engineering problems.

But until recently, most of Walmart’s tech has lived behind the scenes. That’s changed because of smartphones. As Walmart pushes mobile as an integral part of shopping at its stores, the company has started to treat changes at those stores much like app makers handle the rollout of new features.

Case in point: Walmart’s expansion of its iPhone self-checkout option. Walmart said this week that its iPhone self-checkout option is now being tested in 14 markets, up from two when the service debuted last year. As of now, app-based self-checkout is available in more than 200 stores.