O2 (United Kingdom)
Telefónica UK Limited (trading as O2 – stylised as O2) is a telecommunications services provider in the United Kingdom owned by 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 percent 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 were part of the BT Wireless division. This was spun off from the BT Group in 2002 to form a new holding company, mmO2 plc, which introduced the new "O2" brand for the businesses. mmO2 plc was subsequently renamed O2 plc.
O2 plc was purchased by the Spanish telecommunications company Telefónica in 2005 for £18 billion. Under the terms of the acquisition, Telefónica agreed to retain the "O2" brand and the company's UK headquarters. O2 plc became Telefónica Europe.