The trial, which will test how the service works and look at customer take-up, will include live Transport for London (TfL) service updates available to all Wi-Fi users including non-BT customers.
The ticket hall area and Northern and Bakerloo line platforms at Charing Cross Tube station will become the latest addition to the 1.6 million BT wireless broadband hotspots in the UK and will allow customers to connect to the web.
Any passengers with a Wi-Fi enabled device such as a smartphone, laptop, netbook or tablet computer will be able to go online or check their emails while they are passing through the Tube station.
The service is free for five million BT broadband customers with unlimited BT FON Wi-Fi minutes and for BT Openzone customers.
O2, Tesco Mobile, Vodafone and Orange and other Wi-Fi-enabled devices with Wi-Fi minutes in their contracts can also use the BT Openzone network.
Other users can buy a BT Openzone voucher online.
Kulveer Ranger, the Mayor of London's Transport Adviser, said: 'An ever growing commuter populous has been clamouring to be able to check their emails and browse the net whilst on the go.
'This trial at Charing Cross will allow them to do just that whilst on the Tube platform.
'This is an important step towards seeing how this could be achieved and is part of the Mayor's ambition to examine ways in which we can use technology to adapt the city's transport system to meet the needs of those using it.'
Richard Parry, Strategy and Commercial Director for London Underground, said: 'Around 68,000 passenger journeys are made a day at Charing Cross Tube station.
'We hope that our customers will find it useful to have access to the internet while they are using the Tube station during this six-month trial.
'Live service updates will allow passengers to check the status of the Tube and other transport services while they are on the move at the station.'
Chris Bruce, CEO, BT Openzone, said: 'Wi-Fi is rapidly becoming the simplest way for people to access the internet when out and about and with the launch of this trial at Charing Cross we are now giving commuters the chance to enjoy the UK's biggest Wi-Fi network.'
This trial is part of TfL's strategy to use innovative and additional channels in order to make information even more accessible to customers.
The trial is being funded through BT with no cost to fare or taxpayers.
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