In 1999 BT Group acquired Securicor's 40 percent share of Cellnet and the company was later rebranded as BT Cellnet.
BT Cellnet was rebranded as "O2" on 19 June 2002, along with other former BT subsidiaries; Esat Digifone in Ireland, Viag Interkom in Germany and Telfort Mobiel in the Netherlands. The rebranding was supported by a European advertising campaign, which began on 16 April 2002, across all four countries, at a cost of £130 million. The main launch campaign ran from 19 June and was developed by Vallance Carruthers Coleman Priest, working alongside brand consultancy Lambie-Nairn, creators of the "O2" brand identity.
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