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
O2 (UK) of MVNO networks Tesco Mobile and Giffgaff. To apologise for this, O2 announced that it would be giving hundreds of thousands of its customers compensation for the issue. Pay monthly customers received a 10 per cent discount on their bill whereas Pay As You Go users received a 10 per cent refund on their first top up in September. On 24 November 2014, it was reported that BT were in talks to buy back O2, while at the same time BT confirmed that it was also in talks to buy EE. BT subsequently entered into exclusive talks with EE. On