O2 (UK) O2 (UK) Telefónica UK Limited (trading as O2 – stylised as O) is a telecommunications services provider in the United Kingdom, owned by the Spanish multinational Telefónica, and is headquartered in Slough. With 25 million subscribers (as of December 2017), O2 is the second-largest mobile network operator in the United Kingdom after EE, with Vodafone in third place. O2 was formed in 1985 as Cellnet, a 60:40 joint venture between BT Group and Securicor. In 1999, BT Group acquired Securicor's share of Cellnet and the company was later rebranded as BT Cellnet. In June 2000, BT Cellnet launched the world's
The O2 in 2006. As part of the investment programme, naming rights were sold to O2 plc, and 'The O2' became the official name of the project on 25 May 2005. The £6 million per year deal between O2 plc and AEG included priority tickets and reserved VIP accommodation for O2 mobile customers. The service was also made available to premium ticket holders. O2 plc started talks with AEG in 2005 to have its logo and branding placed on the roof of the dome, but this did not take place. AEG have constantly stated that they wish to abolish the 'Dome' name