O2 (UK) 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. In March 2005, mmO2 restructured its shares and the company was relisted as O2 plc. On 30 November 2005, O2 agreed to a takeover by Telefónica, a Spanish telecommunications company, for £17.7
The O2 sound and security technology, including RFID smart card tagging of staff and VIP guests, and digitally managed sound. There are four computer server rooms to provide this technology. The complex is also covered by CCTV and security personnel. Arena visitors and their bags are screened with X-ray machines and metal detectors at the main entrance. The O2 Arena (referred to as the North Greenwich Arena for the 2012 Summer Olympics and Paralympics) is a 20,000 capacity venue, primarily used for live music. It is located at the centre of The O2 and is the first American-style, multi-purpose arena in London.