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 (Ireland) Internet offered 1GB of data and 350 any network texts. Same terms applied as per Freedom talk. In December 2013 the data allowance of 1GB was increased to 7.5GB which O2 advertised as Unlimited Internet. Along with the new price plan O2 also launched a vast amount of prepay addons such as Talk, Text, Data, International Talk and International text. In 2010, O2 underwent a restructuring phase, implementing a number of cost-cutting measures which involved outsourcing internal divisions to external companies. O2's IT division was outsourced to IBM Ireland, while the "Network Operations" division was outsourced to BT Ireland ("who