O2 has switched on London's first 4G network, in a trial running until June.
The LTE network is also the largest such network in the UK, the company said.
Twenty five 4G sites will go live across London this month, providing coverage from Hyde Park to the O2 Arena in Greenwich as well as key areas including Soho, Westminster, Kings Cross and Canary Wharf.
The network will enable users to access superfast broadband comparable to fibre landlines, O2 said. Customers will be able to make use of high speed corporate LAN access, high definition streaming and mobile gaming. A file of 500 MB could be downloaded in under a minute, five times as fast as on 3G.
Ronan Dunne, chief executive at Telefónica UK (which owns the O2 brand), said: "The work we are doing now will lay the foundations for our commercial 4G network when it launches in the UK."
As part of the trial, selected customers will use Samsung B3730 mobile broadband dongles, supporting speeds of up to 100Mbps, as well as 4G personal wireless hotspots and handsets from a number of other vendors. Over 1,000 individuals are expected to take part.
Those trialling the system in business include John Lewis, one of O2's largest corporate customers. The Institution of Engineering and Technology is also part of the trial.
The O2 4G trial will use the 2.6GHz spectrum band under a Test and Development licence granted to O2 by regulator Ofcom. The band supports the maximum 20MHz RF bandwidth for LTE, which allows 4G speeds of up to 150Mbps.
Ofcom's auction of the 4G spectrum is expected to take place later this year.