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) every O2 retail store. On 20 February 2013, Ofcom announced that O2 had been awarded spectrum in the 800 MHz band for 4G LTE coverage, bidding around £550 million for the spectrum. This spectrum came with a coverage obligation from Ofcom, and O2 is obliged to provide a mobile broadband service for indoor reception to at least 98 per cent of the UK population (expected to cover at least 99 per cent when outdoors) and at least 95 per cent of the population of each of the UK nations – England, Northern Ireland, Scotland and Wales – by the end