In 1999, BT Group acquired Securicor's 40 percent share of Cellnet and the company was later rebranded as BT Cellnet.
In 2001, BT Wireless demerged from BT and took the name mmO2 plc. While mmO2 plc was created in 2001, the O2 consumer brand was introduced on 19 June 2002 in the United Kingdom, Germany, Ireland and the Netherlands (where it lasted for only a year before reverting to Telfort). The rebranding was supported by a European advertising campaign, which began on 16 April 2002 across all four countries. Lambie-Nairn created the O2 brand identity.
Spanish telecommunications company Telefónica acquired O2 in the United Kingdom, Ireland and Germany in early 2006.