Berkshire-based Vodafone and O2 go head-to-head today as they both launch high-speed 4G mobile phone data services.
Vodafone, whose headquarters are in Newbury, 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.
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.