O2 (UK) BT subsidiaries: Esat Digifone in Ireland, Viag Interkom in Germany and Telfort Mobiel in the Netherlands. The rebranding was supported by a European advertising campaign, which began on 16 April 2002, across all four countries, at a cost of £130 million. The main launch campaign ran from 18 June and was developed by Vallance Carruthers Coleman Priest, working alongside brand consultancy Lambie-Nairn, creators of the "O2" brand identity. In March 2005, mmO2 restructured its shares and the company was relisted as O2 plc. On 30 November 2005, O2 agreed to a takeover by Telefónica, a Spanish telecommunications company, for £17.7
O2 (UK) certified with the Carbon Trust Standard in recognition of its commitment to reduce its carbon footprint. O2 attained the standard after saving 47,000 tonnes of carbon over the previous three years through its energy efficiency measures, including a £1.4 million distribution of smart metering technology across the company's cell sites, offices and retail stores, and upgrades to more energy efficient systems across its mobile phone network. In addition to distributing energy efficient LED lighting and boiler system controls, the company was also able to reduce energy use by removing air conditioning units from some of its cell sites and reducing