Telefonica and Liberty Global have been working with advisers on the sale of up to half of their combined 50% stake in Cornerstone. Vodafone (VOD.L) owns the rest of the business through its Frankfurt-based subsidiary Vantage Towers (VTWRn.H). Spokespeople for Telefonica, Liberty Global, Virgin Media O2 and GLIL declined to comment. Cornerstone, established in 2012, is Britain's largest tower company, managing more than 20,000 sites, according to the company's website. In recent years infrastructure and private equity investors have competed for slices in some of the largest tower deals, including Deutsche Telekom's sale of a majority stake in GD Towers, because of their stable cash yield and long-term contracts.

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Persons: Phil Noble, Amy, Jo Crowley, Andres Gonzalez, Paul Sandle, Helen Popper Our Organizations: REUTERS, Virgin Media O2, Liberty Global, Telefonica, Cornerstone, Vodafone, Deutsche, GD, Thomson Locations: Blackpool, Britain, Frankfurt