Telefonica UK Limited, trading as O2 (stylised as O 2 ), is a British telecommunications services provider, headquartered in Reading, England which operates under the O2 brand. It is owned by VMED O2 UK Limited, a 50:50 joint venture between Telefónica and Liberty Global. O2 is the UK's largest mobile network operator, with 23.8 million subscribers as of May 2023. Wikipedia