Carphone Warehouse, the mobile phone retailer and telecoms provider, on Tuesday announced plans to further broaden its business activities by launching a big push in the US, widening the remit of its UK stores and rolling out a national home support service.

The company confirmed a Financial Times report that it would start selling mobile phones in 150 to 200 US stores over the next 18 months after a successful trial of its joint venture with the retailer Best Buy in New York.

The majority of these will be “store within a store” formats in existing Best Buy outlets.

Roger Taylor, chief financial officer, said: “[US] customers like what we do, giving them an impartial view.

“The customers’ understanding of tariffs is a long way behind Europe.”

Carphone Warehouse recently launched Geek Squad, a US-inspired home technology support service, in London and said it would roll this out to cover the whole of the UK during the coming months.

It also plans to refit existing UK stores so staff could sell broader “wireless solutions”, such as set-top boxes for televisions and wireless routers for home broadband connections.

Charles Dunstone, chief executive, repeated his targets for Carphone Warehouse’s broadband business.

He hopes to have 3.5m customers signed up to its high-speed internet service by March 2010, compared with 2.27bn at the end of last month.

Capital expenditure for the current year, which ends in March 2008, will be £220m, reflecting the expansion into the US and the spiraling cost of building up its UK broadband business.

Since launching its cut-price TalkTalk broadband service this time last year, Carphone Warehouse has incurred start-up losses of £70m on top of the £370m it paid for AOL’s internet access business in the autumn.

The company warned recently that delays in moving customers on to its own unbundled network would result in extra costs of between £10m and £15m over the current financial year, wiping as much as half from its original £30m forecast for the fledgling division.

It said it expected to raise its dividend by 30 per cent next year.

The company also announced a change in how it presents its financial performance to investors. For the purposes of results, Carphone Warehouse will divide the business into a distribution division, embracing its mobile phone stores and fixed-line business outside the UK, and a UK fixed-line division.

Carphone shares were 3½p lower at 296½p in early London trading.