O2 (UK) Telefónica O2 had a long-standing relationship with Arsenal F.C., being their shirt sponsor until the end of the 2005/2006 season. In 2005, a three-year deal was signed that saw Telefónica O2 become the team's exclusive mobile communications partner. O2 were the main sponsor of the Channel 4 reality TV show "Big Brother" from its second series (as BT Cellnet) in 2001 until its fourth series in 2003. They also sponsored the spin-off shows "Celebrity Big Brother 2" in 2002 and "" in 2003. In total O2 sponsored five series of the show. O2 sponsored music festivals, the Wireless Festivals, from
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,