The iPhone is the new must-have in the fashion and retail world.

Following the lead of Ralph Lauren, Chanel and Sears, more apparel and retail companies are rolling out applications for the iPhone, from shopping to search. If the trend continues, expect shopping via iPhone to be the norm by Christmas 2010.

This story first appeared in the May 29, 2009 issue of WWD. Subscribe Today.

“The sales results have been quite encouraging,” said Yoox founder Federico Marchetti. Yoox put up a test version of its site in April without fanfare, and 710 customers placed orders over their iPhones in the first month. (The orders were from real customers who found the site on their own, not testers.) Yoox plans to officially unveil the site in early June to coincide with a sale of vintage Pucci.

“The concept of combining the past and the future has always been very Yoox,” said Marchetti. “I thought it was the perfect way to put together technology with retail and fashion.” Yoox developed its iPhone site in-house in three months. The retailer also builds and hosts Web stores for clients such as Marni, Pucci and Armani, some of which could have their own iPhone stores by the end of the year, he said.

As smartphones with Internet access such as the iPhone, BlackBerry and the forthcoming Palm Pre become common, it makes sense to adapt Web stores and other sites and create new applications to work on them, said retailers.

“There’s a fundamental shift going on with how people use and interact with the Internet,” said Sears mobile innovations team leader Thomas Emmons. “As more and more devices come out and they get better, we will see a much bigger push into this. We think there’s a strong future in this and that’s why we got involved.”

Sears introduced for all mobile phones last year. Other retailers who offer shopping by phone include SVC and Chanel and Ralph Lauren fans can watch runway shows on their iPhones.

About 20 percent of mobile phones shipped in the U.S. last year were smartphones, for a total of 34 million smartphones of 170 million mobile phones altogether, according to analyst Ramon Llamas of International Data Corp. in Framingham, Mass. He predicts smartphone sales will increase this year even as sales of all mobile phones decrease slightly, to 37 million smartphones and 150 million mobile phones.

A Web site or application that has been optimized or written specifically for the iPhone is easier to use on the device and can take advantage of specific iPhone features such as geolocation, said Demandware vice president of marketing Jamus Driscoll. For example, a regular Web page may be somewhat difficult to read on the narrower iPhone format, and shopping carts and checkout may not work.

Demandware is prototyping a shopping cart application for the iPhone now, which might be available to clients early next year, he said. Demandware is an e-commerce service provider with customers including Barneys New York, Nine West, Bare Escentuals, Crocs and Timberland.

The company is investigating how to streamline checkout on the iPhone by using iPhone menus and navigation features to select color and size. Transactions will take place on Demandware’s servers and take advantage of the service’s security.

Driscoll advised retailers to get iPhone stores up by spring or summer next year. “The guidance we’re giving our clients is if you wait for holiday 2010, it will be a little too late,” he said.

Fashion search site ShopStyle this month introduced an iPhone version of its service that displays fashion images in tic-tac-toe format, horizontally or vertically. The simple menu lets browsers e-mail an item, click to read more details or click to buy.

“At the beginning, we imagine most people will be e-mailing it and completing the purchase online because it’s still cumbersome to make a purchase on most retailers’ sites,” said Brian Sugar, chief executive of Sugar Inc., which owns ShopStyle.

A forthcoming version of the application will add sales alerts and favorites.

Sugar is also developing other iPhone applications, such as a celebrity game that ties into its PopSugar blog.

“I think mobile will be something that matters,” said the ceo. “It gives visibility to ShopStyle. I’m a firm believer that everything you can do on a desktop now you will do on an iPhone in a few years.” For example, people can comparison shop or browse for dresses online while they are walking around shopping in stores, he said.