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Phone company Three will attempt to make up for its late entry into the 4G network battle by offering customers an upgrade to the high-speed service for free.
The company said a "simple software upgrade" would be made available "at no extra cost" upon its launch in London, Birmingham and Manchester in December.
The service will be available in 50 cities by the end of 2014.
Like rivals Vodafone and O2, who launched 4G services today, and high-speed frontrunner EE, the company's reach will grow to 95% of the UK by the end of 2015.
Guy Laurence, chief executive of Vodafone UK, has predicted a swift take up for 4G as people crave faster downloading speeds to enjoy music, videos and live streaming.
"I think adoption will be far faster than 3G, which was 10 years ago, because people didn't really know how to use it," he said.
"It is no good trying to sell technology to people, you have to sell something they want, and they want entertainment."
Mr Laurence said 4G will be on tap for nearly all of Britain within 18 months.
"By the end of 2015 we will have 98% coverage," he said. "To give you an idea, only 98.4% of dwellings have running water. So 98% is very high indeed."
EE has had a 10-month headstart on phone rivals Vodafone and O2 after winning the right to launch 4G coverage in the UK.
EE's mobile internet service began in October and now covers 60% of the UK population.
The phone company yesterday crowned Accrington in Lancashire the 100th town in Britain to receive the "super-fast" service.
While today's launch of 4G services by O2 and Vodafone will be limited, both aim to have 4G network coverage in 13 cities by the end of the year and eventually serve 98% of Britain.
O2's service will initially be switched on in London, Leeds and Bradford, reaching up to five million people. Vodafone will roll its service out in parts of the capital.
The phone companies will then expand to London, Birmingham, Bradford, Coventry, Edinburgh, Glasgow, Leeds, Leicester, Liverpool, Manchester, Newcastle, Nottingham and Sheffield.
Vodafone and O2 go head-to-head today as they both launch high-speed 4G mobile phone data services.
Vodafone will offer 4G to its customers in London, while O2 launches its service in London, Leeds and Bradford.
The mobile giants will compete against EE, which has been the only company offering super-fast mobile data in the UK.
Latest ITV News reports
O2 and Vodafone's venture into the speedy download market means more competition and a possible price war. But the battle goes beyond costs.