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 Czech Republic different lines of business: the retail operator O2 and the wholesale infrastructure provider CETIN. The separation includes commercial and managerial leadership and management of both companies, including security, IT and control systems. The company was initially known as SPT Telecom ("Státní telekomunikační podnik", state-owned telecommunications company), and used to have a monopoly for providing fixed-line services. It was reorganized and renamed Český Telecom (Czech Telecom), after the Velvet Divorce saw Czechoslovakia separate into the Czech Republic and Slovakia in 1993. Its mobile subsidiary, Eurotel, was founded in 1990 as a joint venture between SPT (51%) and the American joint-venture Atlantic