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) better, connected", in 2013 to "Be more dog", and in 2016 to "More for you". All of O2's marketing campaigns to date have been created by London advertising agency VCCP. "O2 Priority" offers benefits to customers including early access to tickets for events at the O2 Arena and O2 Academy venues. "O2 Refresh", introduced in 2013, splits monthly billing into two parts so customers pay for their device (phone or tablet) separately from their airtime. From 2017, customers can change their airtime tariff up or down, once a month, during the first 24 months of their contract. O2 currently sponsor