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 Arena The O2 Arena The O2 Arena is a multi-purpose indoor arena located in the centre of The O2 entertainment complex on the Greenwich Peninsula in south east London. The arena was built under the former Millennium Dome, a large dome shaped building built to house an exhibition celebrating the turn of the third millennium; as the dome shaped structure still stands over the arena, "The Dome" remains a name in common usage for the venue. The arena, as well as the total O2 complex, is named after its primary sponsor, the telecommunications company O. The O2 Arena has the second