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
PageOne Communications new name 'PageOne Communications'. 1992 - Mercury Paging Ltd acquires Intercity Paging ltd. Intercity's owner, Mtel Corporation (US) becomes the third shareholder. In the same year Mercury Paging's paging network infrastructure underwent extensive investment with satellite distribution technology implemented nationwide. 1990 - Using a single UK paging license, Mercury Paging commenced trading. A second UK paging channel was allocated in 1990. 1986 - PageOne Communications incorporated under its former name of Mercury Paging Ltd, its parent company, Mercury Communications being jointly owned by Cable and Wireless and Motorola. PageOne (operating under the Mercury brand) was the first UK organisation to