O2 (351 Oxford Street)

Telefónica UK Limited (trading as O2 – stylised as O2) is a telecommunications services provider in the United Kingdom, owned by the Spanish multinational Telefónica. It is the second-largest mobile telecommunications provider in the United Kingdom after EE Limited, and is headquartered in Slough. O2 was formed in 1985 as Cellnet, a 60:40 joint venture between BT Group and Securicor. In 1999, BT Group acquired Securicor's 40 per cent share of Cellnet and the company was later rebranded as BT Cellnet. In June 2000 BT Cellnet launched the world's first commercial General Packet Radio Service. BT Cellnet, together with BT Group's mobile telecommunications businesses in Germany, Ireland and the Netherlands, was part of the BT Wireless division.