Just a few years ago, retailers considered smartphones the enemy of the in-store experience. Customers often whipped out their devices to compare prices online and then walked out of the store to buy the same product elsewhere.

Today, stores consider the smartphone their friend. Their smartphone apps let customers do things like scan and pay, as well as download digital maps — and replicate the online experience.

Nike created a buzz last month when it unveiled two features on its mobile app. One lets shoppers see details of every item displayed on a mannequin by scanning the QR code next to it. They can even have the items delivered to a fitting room or a pickup spot without ever talking to a clerk. Another feature, instant checkout, lets customers scan the barcode of an item, pay via credit card, then walk right out of the store.

But there’s room for improvement. Stores need to do a better job of promoting their mobile checkout while working out the kinks. They also need to make their in-store Wi-Fi service more reliable, analysts say.

Three problem areas:

>> Mobile checkout: At stores like Walmart and Target, shoppers can only use mobile checkout for a limited number of items; if they have a cart full of products, they’ll need to still go the cash register. And unlike Nike, few stores are heavily promoting the service. At Macy’s, shoppers can scan and pay for items on their smartphones but must then go to a mobile checkout express line or a regular cash register to have security tags removed from clothing.

Spotty Wi-Fi: Service needs to be more reliable to handle all the digital content and services. Analysts say connections are still spotty and inconsistent, and service gets worse when the store is crowded.

Unreliable pickup service: Analysts say shoppers often walk in to pick up online orders to find they aren’t ready. Anthony Karabus of HRC Retail Advisory, a consultancy, surveyed 30 top retailers and found a discrepancy between the items that store websites tell shoppers are in stock versus what a particular store actually has on hand.