A digital radio communications system for the police is now fully operational in all London's Underground stations.
It comes after a London Assembly report in 2006 said poor communication had hampered rescuers after the 7 July 2005 terror attacks on the transport system.
Fire crews and ambulance staff use similar systems, although neither has been fully deployed.
Meanwhile, concerns have emerged about whether the police network will cope with demands during the 2012 Olympics.
The Commons home affairs committee has said the network "struggles" when large numbers of users are concentrated in the same area.
And a security source told the BBC the system could collapse as demand is expected to increase in 2012 by 25-30%.
Experts, however, are preparing to equip Airwave with extra capacity in time for the London Games.
It is understood the deployment of Airwave handsets to all ambulance staff is still taking place.
Fire Brigade units have a system they say works underground and is inter-operable with Airwave.
Policing Minister Vernon Coaker said the Airwave system for police had been delivered "ahead of schedule".
He said: "The Airwave system plays a vital part in keeping passengers safe.
"It allows police officers to communicate with each other quickly and safely to ensure an effective response to any incident."
The system, already used above ground, has now been deployed across the network of tunnels and 125 below-ground Tube stations.
Tony McNulty, Minister for London said: "One of the key lessons from the London bombings of 2005 was the need to enhance the resilience of responders' telecommunications systems and communication underground."
Only the British Transport Police were able to communicate underground by radio after the terror attacks at Aldgate, Edgware Road, Russell Square and Tavistock Square.
This was despite the fact a report into the King's Cross Underground fire more than 21 years ago had recommended that action was taken to improve the radio system then.
London Underground's own radio system - described as "very old" by the organisation's own managing director Tim O'Toole - also broke down during the response.
Since then, Transport for London (TfL) said it would be investing more than £2bn over 20 years in its Underground digital radio network, called Connect.
Airwave now "piggy-backs" on that digital system and for British Transport Police, removes the need for officers to carry two radios - one for above ground, one for below.
Supt Alex Carson, of the British Transport Police said: "The fact that Airwave provides coverage within the tunnels and not just the stations brings real benefits in terms of officer safety and operational effectiveness.
"When escorting football fans on the Underground officers are no longer out of radio coverage when the train leaves the station.
"This means officers can be deployed to potential trouble spots far quicker than before."
Chief executive of the National Policing Improvement Agency (NPIA), Chief Constable Peter Neyroud, said: "I went down to the deepest point of the Tube, 35 metres below sea level, and I was astonished at how good the sound was.
"It was as good as being stood on the street."
A London Assembly 7 July Review Committee report in 2007 highlighted outstanding issues relating to coverage and timing of the deployment of the Airwave radios.
Chairman of the review committee Richard Barnes said at the time: "Londoners can be reassured that... no-one is being complacent about their ability to respond to such a horrific incident.
"Our report highlights continuing problems with Airwave that need to be tackled."
London's underground network of 270 stations has 249 miles (402km) of track, of which 112 miles (181 km) is in tunnels.