Seventy organisations have registered interest in providing the technology that will enable commuters to use their mobile phones in Tube stations.
Passengers will be able to use their phone at stations from mid 2008
In March, Transport for London (TfL) said mobiles would be able to work in stations from mid-2008 and a trial could be held at a station next year.
The deadline for interested firms to respond was extended by a month due to a high level of interest.
A contract could be awarded in late 2007, TfL said.
London Underground's (LU)Richard Parry said: "We have received an excellent initial response from the market who have demonstrated considerable interest in providing both mobile phone services and other exciting technologies for LU customers."
After the scheme is introduced in summer 2008, mobile phone services and the additional technologies could be extended across the network at a later date in order to make mobile phones work in tunnels and on moving trains.
Passengers using deep-lying stations may also be able to access the internet on laptops and other devices.
All interested firms should have their responses in to TfL by the middle of June.