O2 (UK) Telefónica O2 had a long-standing relationship with Arsenal F.C., being their shirt sponsor until the end of the 2005/2006 season. In 2005, a three-year deal was signed that saw Telefónica O2 become the team's exclusive mobile communications partner. O2 were the main sponsor of the Channel 4 reality TV show "Big Brother" from its second series (as BT Cellnet) in 2001 until its fourth series in 2003. They also sponsored the spin-off shows "Celebrity Big Brother 2" in 2002 and "" in 2003. In total O2 sponsored five series of the show. O2 sponsored music festivals, the Wireless Festivals, from
O2 (UK) manufacturing Near Field Communication (NFC) technology in mobile phones in the United Kingdom. O2 and Vodafone signed a deal in June 2012 which will see the two companies 'pool' their network technology, creating a single national grid of 18,500 transmitter sites. Both networks will continue to carry their own independent mobile spectrum. In July 2012, O2 had to apologise to almost 8 million customers after a network switching subsystem failure led to a 24-hour blackout of the service across the UK and Ireland. The problem, which prevented a third of its customers' phones registering on the network, also affected customers