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) in Germany were brought under the control of O2, which retained its UK-registered public company status with its own board of directors and corporate structures and processes. Telefónica chose to keep its existing mobile phone operations in the rest of the world under the brand Movistar. This name is used in Spain and in most of the Latin American countries, operated by a separate management team. On 15 July 2009, O2 entered the financial services industry with the launch of O2 Money, which was the first step in the process of incorporating financial services into mobile phones. Future plans included