Optus says the project that brought mobile phone coverage into Sydney's train tunnels was 15 years in the making.
Speaking at the launch announcement of the company's new multi-band 4G rollout, Optus' vice-president of mobile engineering, Andrew Smith, said the required approvals to implement the technology in the railway network took up to 15 years.
"It's taken that long to get the approvals, we got a lot of support from the incoming state Government to push it through," he said.
"One of the real issues was always safety because we are building systems inside tunnels, and also the age of those tunnels. That was a big part of the barrier of being able to satisfy the railways that we can implement a safe solution in association to the agreements."
"We've had collaboration from the carriers to get a solution in there so it's not a competitive issue, but it's been quite a challenging road. We were in a position where the support level went up and that started to get things rolling. You need lots of maintenance access and things like that which you can't just expect to get."
As part of the initial rollout which began in July last year, the North Shore and Western Lines of the CityRail network were the first to receive mobile coverage through tunnels between Central and Chatswood stations.
The service was then extended to all train tunnels on the City Circle line in April this year.
"The tester was that North Shore segment, that was a big thing for us to work with the railway and they were pleased how we worked with them. We moved very, very quickly in the City Circle and now we are working on the Eastern Suburbs line. There will be other segments beyond that but that's sort of our three stage plan."
Optus has not committed to an estimated completion date for tunnels on the Eastern Suburbs Line. This latest rollout requires 18 kilometres of cable between Erskineville and Bondi Junction stations.
The overall mobile network rollout is a three way partnership between Optus, the NSW Government and RailCorp, a an agency of the Government responsible for the operation and maintenance of Sydney's CityRail train network.
From Monday 1 July, RailCorp will be broken up and split into two new specialist organisations. Sydney Trains will serve regular, suburban line services while NSW Trains will be responsible for all intercity, regional and country services.