RETAILER Phones4U has been sold in a deal thought to be worth up to £700m.

The sale also triggers a second pay-out for founder John Caudwell.

The company, which has more than 500 stores in the UK and employs about 6,000 staff, is to be snapped up by Fitness First owner BC Partners.

The retailer, which reported a 20% increase in sales to £900m in 2010, is mainly owned by US-based investor Providence Equity although Mr Caudwell and the management team still hold a 25% stake.

The deal – believed to be worth between £600m and £700m – comes just a few months after Providence snubbed several offers for the business.

The sale will net Mr Caudwell a further windfall in addition to the £1.46bn he made by selling 75% of the company and his 20:20 distribution arm to Providence in 2006.

Andrew Newington, managing partner at BC Partners, said Phones4U’s strong brand and extensive store network meant it was well-positioned to benefit from further strong growth in the smartphone market.

Phones4U claims to sell one in every four contract smartphones on the high street and said its advertising campaigns and marketing on social network sites helps it connect with the hard-to-reach youth market.

The company last year unveiled a deal with Currys owner DSG International to open branded “Phones4U at Currys” outlets in at least 50 stores after trials in five UK megastores.

Providence recently said Phones4U was expected to generate underlying earnings of £130m in 2010 – up by 23% on the previous year – although it holds debts of £300m.

It received numerous expressions of interest for Phones, but ruled itself out of a sale in December, saying it could “realise the most value through its continued ownership” of the company.

The group began as Midlands Mobile Phones in 1987 when Mr Caudwell bought 26 phones from the US for more than £1,000 each and sold them on in the UK.

He sold the company in 2006 to Providence in a deal that included the disposal of 20:20 to UK-based private equity firm Doughty Hanson.

BC Partners also owns a stake in Intelsat, the world’s leading provider of fixed satellite services.