Three UK, the last mobile operator to launch 4G in the country, quietly launched the network on Monday, but only to a few thousand customers in London.
The operator announced plans in August to launch 4G in December across London, Birmingham and Manchester, however an update today suggests it might be a few months off schedule.
In a statement today, Three said it began the rollout on 2 December, but, according to an update on ThreeUK's Twitter account, 4G has so far only been enabled for a "few thousand customers" in London.
The broader rollout will happen sometime between January and February next year. Three said it will accelerate its 4G rollout in January with plans to reach all customers in the areas initially scheduled by the end of the first quarter next year.
Despite the slow start, Three still aims to cover 50 cities by the end of 2014 and 98 percent of the population by the end of 2015. The operator currently has 7.8 million active customers in the UK, which is down 9.7 percent from a year ago.
Three was the first to launch its 3G network back in 2003, but is lagging its UK rivals EE, Vodafone and O2 in the current 4G roll out.
Unlike its competition, Three will automatically make its 4G network available to all customers with a 4G device and will not charge additional fees for it - good news for Three's contract customers who have already bought Google's Nexus 5 and Apple's iPhone 5c and 5s from the operator.
EE, the first 4G operator in the UK, covers around 60 percent of the country and has one million 4G subscribers, according to September figures. More recently, EE has been trialling LTE Advanced, which offers theoretical speeds of 150Mbps.
Vodafone and O2 switched their networks on in August. Vodafone is targeting 98 percent coverage by population for its 4G network by the end of 2015.