O2 (UK) they can do it too" in reference to Vodafone and EE, O2's biggest competitors and the UK's top three mobile-telecoms companies. O2 (UK) Telefónica UK Limited (trading as O2 – stylised as O) is a telecommunications services provider in the United Kingdom, owned by the Spanish multinational Telefónica, and is headquartered in Slough. With 25 million subscribers (as of December 2017), O2 is the second-largest mobile network operator in the United Kingdom after EE, with Vodafone in third place. O2 was formed in 1985 as Cellnet, a 60:40 joint venture between BT Group and Securicor. In 1999, BT Group acquired
GTT Communications GTT Communications GTT Communications, Inc. (GTT), formerly Global Telecom and Technology, is a multinational telecommunications and internet provider company with headquarters in McLean, Virginia. GTT operates a Tier 1 IP network, and provides IP transit, MPLS transport services, managed services, voice and unified communications to enterprise, government, and carrier customers in over 100 countries. In 1998, telecom services integrator and network solutions provider Global Internetworking Inc. was founded in McLean, Virginia. That same year, European Telecom and Technology was founded in London. In April 2005, Mercator Partners Acquisition Corp., a special purpose acquisition company created by Reston-based investment bank Mercator