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) computer monitor standby times. O2 is a voluntary participant in the climate change campaign, which required participants to cut their carbon emissions by 10 per cent by the end of 2010, and has since broadened its approach to include a range of projects focused on carbon reduction and renewable energy. In October 2017, an inquiry was launched in the UK concerning overcharging customers for handset sales integrated with the data and call charges. Responding to questions, O2's CEO indicated that the company's billing allows for separation of handset charges and telephony/data charges. He added that "if we can do it,