Best Buy is looking to ring up more market share gains now that it has added mobile phone shops to all of its U.S. stores.

The electronics chain has completed the rollout of Best Buy Mobile shops at its 965 U.S. stores – three months ahead of schedule.

The mobile shops offer a wider assortment of handsets and monthly as well as pay-as-you-go service plans. Consumers can select from Sprint, Verizon Wireless, AT&T and other carriers.

Shawn Score, Best Buy Mobile president, said market share gains in the first Best Buy stores that added the mobile departments inspired the quicker national rollout.

“About a third of our stores is producing the current share gains we’ve got,” Score said in an interview. “We are up at least 50 percent in our market share in each of the last six months.”

Banc of America Securities analyst David Strasser said in a recent research note that the Best Buy Mobile expansion was likely a factor in wireless market share losses at rival RadioShack during the second quarter. “We believe Best Buy Mobile will only become a stronger competitor as they ramp up,” Strasser said.

There are also about 15 standalone Best Buy Mobile shops in the United States now, with plans to have at least 35 up and running before the holidays, Score said.

The mobile shops, a joint venture with Britain’s Carphone Warehouse, are part of Best Buy’s strategy to double annual sales by expanding in traditional electronics categories as well as moving into new areas. For example, Best Buy now has musical-instrument shops in some of its stores.

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