UK mobile phone retailer the Carphone Warehouse said Tuesday that it will launch a business in the US following a five month trial with electronics store partner, Best Buy.

The retailer said it will expand the concept of Best Buy Mobile on a commercial scale, with 150-200 stores to be opened over the next 18 months. The majority of these will be ‘store within a store’ concepts in existing Best Buy locations.

In Europe, Carphone said it also plans to open 250 new stores this year as well as investing in up to 100 major re-sites or refits in major locations.

All in all, the retailer expects to spend around £60m on new stores, re-sites and refits and around £20m on joint ventures.

Charles Dunstone, chief executive officer of CPW, said, “Our US trial has been successful and we are today announcing a rapid roll-out of the Best Buy Mobile format, allowing us to penetrate the substantial US market in an effective manner.”

Counting 1.5 million fixed broadband subscribers as of the end of March, Dunstone said, “We are targeting 3.5 million residential customers by March 2010. Provisioning times are falling as the unbundling process becomes more streamlined, and we are confident that our increased investment in customer service will deliver a much improved customer experience.”

Reports today suggest that CPW will not be in a position to clear the backlog of 260,000 broadband customers currently waiting to get connected until October.