• Wall Street Journal, Thursday, December 16, 2010 10:26 AM

Although smartphone fans remain a small part of all shoppers, marketers must contend with those who use them inside stores to check on prices and compare them to the competition's.

"The retailer's advantage has been eroded," Greg Girard of consultancy IDC Retail Insights tells the Journal. IDC recently found that roughly 45% of customers with smartphones had used them to perform due diligence on a store's prices. "The four walls of the store have become porous."

Among those most vulnerable are retailers of branded, big-ticket items such as electronics and appliances. Even Best Buy has been impacted by the practice, saying it may lost share this year, in part due to price comparison apps.

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