Mobile Phone Technology

O2 is one of the three UK mobile phone operators. It is owned by Virgin Media and operates under the Virgin Media O2 brand. O2 is the smallest of the UK operators, holding 26% of the market. This includes Virgin Media Mobile customers as well as O2 customers.

O2 has several available frequencies, including 800 MHz for 4G and 700 MHz and 3.4–3.8 GHz for 5G. They also have some mid-range frequencies (1800 MHz and 2100 MHz) that they use for 4G or 5G, which were re-farmed from 2G and 3G. As of 31 December 2025, O2 still operates some 3G communications, but these will be switched off for consumers very soon.

O2 is one of the UK's two original mobile operators, originally called Cellnet and owned by BT. They ran a 1G analogue network throughout the UK. Following the release of the digital 2G network, Cellnet became one of the four mobile network operators. The network was later sold to Telefónica, who changed the name to O2. O2 also participated in the 3G auction and became one of the four UK 3G operators to be awarded a contract.

O2 also operates a substantial 4G network across the entire UK. Over the years, O2 has accumulated a lot of frequency in a number of spectrum areas due to various spectrum auctions and Ofcom allocations. Perhaps because of this, O2 did not purchase any 2.6 GHz spectrum to run their 4G network. However, as part of the latest 5G auctions, they purchased some 2.3 GHz spectrum to expand their 4G capacity.

In the 5G auction, they purchased 3.4 GHz and 3.6 GHz spectrum to provide 5G capacity, as well as 700 MHz spectrum to provide 5G coverage. Following the auction and some frequency adjustments, O2 now has a continuous block of 80 MHz for 5G use. Although O2 was the last to switch on a 5G network, they now have a 'full' 5G service throughout the UK. Unlike the other mobile operators, O2 was not significantly exposed to Chinese equipment from Huawei and ZTE, and therefore did not incur the costs or delays caused by removing this equipment from the network.

The O2 network was recently sold to Virgin Media, creating the Virgin Media O2 brand. Under Virgin Media ownership, O2 is part of an organisation with a significant digital entertainment offering, as well as its own broadband and fibre infrastructure, and it is also a mobile operator. Due to this range of offerings, Virgin Media-O2 is a direct competitor to BT/EE.

O2 has a large online and retail presence, selling mobile phones and other devices that can be connected to its network.

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