People travelling on London's Tube network may be able to talk on their mobile phones even when deep underground by the end of the year.
Using mobile phones may be possible on the Tube
BBC London has learned that London Underground (LU) has been in negotiation with the four main mobile phone companies.
It means a new series of underground transmitters will be installed in stations and potentially in tunnels.
The technology is already in use on the Tyne and Wear Metro system.
BBC London's transport correspondent Andrew Winstanley said the system would have to be fully tested in London's far more extensive network.
The Tyne and Wear Metro has only four miles of tunnels whereas London's Tube has 130 miles of tunnels.
Travellers 'in favour'
But Metro engineers are said not to foresee too many problems and it has worked well in Newcastle.
LU's Richard Squire told BBC London: "So many people have got mobile phones, we feel from a customer services point of view we're going to have to do this."
LU has conducted a series of surveys among its passengers and most have welcomed the system as long as people were sensible and respected the space and privacy of other travellers.
The system could also make money for LU because Orange, O2, T-Mobile and Vodafone would have to rent the space the equipment occupies.