Unless you live in Britain, you may never have heard of the retailing phenomenon known as Carphone Warehouse. From its modest launch less than 20 years ago the seller of mobile handsets and services has grown into an industry giant, with 2,300 stores across Europe offering the widest range of products — and often the best prices.

Now, the London company is poised to leap across the Atlantic, thanks to a joint venture with electronics chain Best Buy. Starting this year, Carphone Warehouse will roll out nearly 1,000 outlets in the U.S., some of them boutiques inside existing Best Buy stores and others standalone storefronts. Best Buy also owns a 3 percent stake in Carphone Warehouse.

American mobile operators should pay close attention. Carphone Warehouse revolutionized the industry in Britain by being the first seller of phones and mobile services not affiliated with any carrier or handset maker. That allowed consumers to compare prices and service plans from many providers — and ratcheted up market competition among the players. The novel business model made Carphone, as it’s popularly known, a hit with buyers confused by the bewildering variety of mobile service plans and prices.

Giving Customers What They Want

Since then the company has pioneered one retailing innovation after another. It has launched its own name-brand telecom services — including fixed-line, mobile, and broadband access — and rolled out training programs that help consumers get up to speed quickly on new gadgets.

“Carphone has been a big innovator in the telecom market,” says Richard Perk, director of retail research at London research firm Mintel. “It does what no other major [tech] retailer can do, offering independent advice and additional services that customers really want.”

Perhaps the most crucial realization by Carphone founder and Chief Executive Charles Dunstone was that selling a phone or other gadget was…