A Mobile Network Operator (MNO), also known as a mobile network carrier, is a provider of the infrastructure upon which mobile services are delivered. When a mobile customer requests a mobile service this is delivered by one of the available MNOs; be that service a phone call, SMS message or mobile data request.

There are four MNOs in the UK, in size of customer base order :

• EE - which is owned by BT.
• O2 - which is owned by Telephonica.
• Vodafone
• Three which is owned by Hutchison Telecoms Group.

These four companies provide the mobile network within the UK. They purchase, the licenses, setup the network and manage the services provided. In addition, there are a number of Mobile Network Virtual Operators in the UK. These organisations pigy-back on one of the four mobile network operators.

A bit of history.

• Vodafone was one of the two original operators for mobile phones in the UK and has been in the market from the original 1G to the forthcoming 5G. Vodafone is a company listed on the UK stock market
• The other original 1G mobile network operator was Cellnet owned and run by BT. This was was rebranded as O2 and sold to Telefonica later when BT took the commercial decision to move out of the mobile phone network business. O2 continues to operate and has a 5G MNO license
• At the allocation of the 2G licences another 2 operators were allowed into the market. One being Orange. This company operated 2G then 3G networks prior to being merged, with T-Mobile into EE. Orange still operate under the name in various countries in Europe.
• The other new company to come into the mobile phpne market when 2g licences were allocated was one-to-one, who originally only operated within the M25 area. They then moved nationally, and later merged with Orange to form EE. Again T-Mobile operate in Europe as T-Mobile
• Three, owned by Hutchison Telecom, were allocated a 3G network license as as new operator into the market. This company has moved on from3g to 4G and now have a 5G license
• With the allocation of 4G licenses, BT moved back into the marker when they bought some bandwidth. In a reverse of their previous decision, they decided to move back into the mobile phone market in a big way and took over EE to add to their own allocaton of mobile bandwidth