O2 UK (legally Telefónica UK Ltd.) is a telecommunications services provider in the United Kingdom, owned by Telefónica, headquartered in Slough, England.
O2 was formed in 1985 as Cellnet, a 60:40 joint venture between BT Group and Securicor. In 1999, BT acquired Securicor's share of Cellnet and the company was later rebranded as BT Cellnet.
BT Cellnet relaunched as "O2" on 18 June 2002. In 2006 the company was purchased by Telefónica, who retained the O2 brand and the company's UK headquarters.
In June 2000, BT Cellnet launched the world's first commercial General Packet Radio Service (GPRS) service.
General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM).
GPRS is a best-effort service, implying variable throughput and latency that depend on the number of other users sharing the service concurrently, as opposed to circuit switching, where a certain quality of service (QoS) is guaranteed during the connection.
With 34 million customers (including those on MVNO networks) as of February 2020, O2 is the largest UK mobile network operator, followed by EE, Vodafone and Three.
According to en.wikipedia