<P> After months of rumours and speculation, Peter Bonfield publicly announced on 27 July 1999 that BT had agreed to buy Securicor's 40 per cent share of Cellnet for £ 3.15 billion . Cellnet had five million customers at the time of its acquisition . The company was later rebranded as BT Cellnet, and it became a part of BT Wireless, a group of companies owned by BT . </P> <P> BT announced on 3 September 2001 that the BT Wireless business would be spun off from the main group as a newly listed holding company, mmO2 plc, operating under the "O2" brand . Shareholders approved the plan at an extraordinary general meeting on 23 October 2001 . </P> <P> BT Cellnet relaunched as "O2" on 18 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 18 June and was developed by Vallance Carruthers Coleman Priest, working alongside brand consultancy Lambie - Nairn, creators of the "O2" brand identity . </P> <P> In March 2005, mmO2 restructured its shares and the company was relisted as O2 plc . </P>

What does the o in o2 stand for
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