BBC Technology reports that Everything Everywhere, which will now be known as just EE, will continue the rollout into the new year, and aims to provide 4G to 98% of the country by 2014.
Belfast, Glasgow, Liverpool, Manchester and London are among the cities chosen.
Rivals have voiced concerns that EE has been given an unfair headstart by launching first.
Other cities to get the high-speed connectivity are Leeds, Nottingham, Newcastle, Sheffield, Southampton, Birmingham, Bristol, Cardiff, Derby, Edinburgh and Hull.
4G mobile technology will mean all of these locations will benefit from improved network access speeds, even indoors.
Further rollout could prove a boon to rural areas where fixed line broadband speeds are poor.
EE won permission to launch 4G services in an Ofcom ruling published on 21 August. In November 2011 it asked Ofcom for permission to run the high-speed data services over part of the radio spectrum it already uses for earlier generation technologies.
Rival networks are being forced to wait to launch their 4G services as they do not have any spare spectrum to use.
All operators will get a chance to buy spectrum to support 4G in 2013 when Ofcom runs an auction to divide up the radio frequencies reserved for these services.
The threat of legal action has delayed the auction and led to the UK trailing many other nations that already have fast-speed 4G services up and running.
The day after EE's launch, Apple is holding an event at which it is thought to be unveiling the next version of its iPhone.
This will also be able to handle 4G but it is not yet clear if it will work on the frequencies that EE's early services will use.