The operator has said its superfast network will cover 98 per cent of the population by the end of 2015
Three has announced its 4G roll out will start in London, Birmingham and Manchester in December.
The news comes on the same day as O2 and Vodafone switch on their 4G networks.
The operator has today (August 29) repeated its promise that it will not charge customers extra for 4G. It is the only one not to charge a premium, with EE, O2 and Vodafone all pricing 4G at about £5 more than 2G and 3G.
Three is also the only operator which will offer unlimited 4G data plans.
It said its 4G network will cover 98 per cent of the population by the end of 2015. EE is aiming for 98 per cent coverage by the end of 2014, while O2 and Vodafone have said their superfast networks will cover 98 per cent “by 2015”.
Following a December launch, Three said rollout will “accelerate” in January so that 1.5 million customers will have access to the service.
To upgrade to 4G, Three customers with a 4G device will need to instal software, and do not need to sign a new contract, change tariffs, swap SIMs or visit a store.