Three says its 4G super-fast mobile data services will be available from December to users in London, Birmingham and Manchester, a wider roll-out will then follow in January.
4G networks will allow operators to offer ultrafast mobile broadband services to consumers and businesses.
In February Three announced that users would enjoy superfast 4G mobile data speeds at no extra cost.
This is in contrast to rivals EE, O2 and Vodafone who are charging customers a premium for their 4G plans.
Three’s announcement comes on the same day O2 and Vodafone launched their services, EE’s 4G network went live last October however high prices meant the company struggled to attract large numbers of subscribers.
4G services require a compatible handset but not all 4G-capable phones can be used on all networks.
For example, O2’s decision to bid for capacity in the 800Mhz band means its 4G network will be unable to support Apple’s iPhone 5.