Ralph Whitworth, the activist investor, is joining the board of Sprint Nextel, a move that gives him a bigger platform to put pressure on management to improve the performance of the struggling US telecoms group.

Mr Whitworth’s investment firm, Relational Investors, owns a stake of about 2 per cent in Sprint. The company’s new chief executive Dan Hesse has been keen to avoid a public confrontation with the investor.

Mr Whitworth, who last year raised pressure on Home Depot to oust Bob Nardelli as chief executive, has been a vocal opponent of Sprint’s plans to spend billions of dollars to build a US high-speed wireless network using nascent WiMax technology.

He has argued the company should focus on reviving its mobile phone business, which is the third-largest in the US but has been losing subscribers for months, and solving the problems caused by the takeover of Nextel Communications.

”A turnaround at Sprint Nextel won’t be easy, but I believe the ingredients are in place to get the job done for the company’s shareholders,” Mr Whitworth said in a statement.

Sprint shares have lost more than 60 per cent since the Nextel deal in 2005.

Unlike other activists who prefer to put pressure on management from the outside, partly because they want to retain the ability to buy and sell shares freely, Mr Whitworth and his associates have often joined boards of target companies such as Home Depot and Sovereign Bank of Pennsylvania.

Mr Whitworth will be in a minority on the 12-strong board, which includes executives from the media, telecoms and defence industries. But his presence, allied with his pugnacious style and financial expertise, is likely to give him some influence on Sprint’s future direction.

The appointment comes at a crucial time for Sprint and Mr Hesse, who became chief executive in December.

Mr Hesse replaced Gary Forsee, who resigned in October under pressure from the board, and immediately launched a strategic review of WiMax, an emerging “fourth generation” technology aimed at offering faster wireless connections.

After scrapping talks over a $5bn WiMax joint venture with Clearwire, a smaller technology group, Sprint is believed to be looking at ways of offloading some of the costs of the project.

Sprint’s options are believed to include spinning off the business in order to attract outside funding from companies that could include Intel, the retailer Best Buy and Google.

Sprint recently announced larger-than-expected subscriber losses and said it would cut about 4,000 jobs. Wall Sreet is bracing for further bad news when it reports its yearly results on February 28.

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