Telstra and Optus have completed phase one of a network expansion that will see mobile coverage brought to commuters in Sydney's City Circle and Eastern Suburbs rail tunnels.
The telcos have switched on network equipment that provides coverage on the North Shore line between Central Station and North Sydney.
Further expansion of coverage in tunnels — including the City Circle loop — is expected later this year.
Telstra said it had rolled out dual-channel HSPA+ technology but would upgrade to LTE "soon". Optus has also rolled out 3G technology.
A spokeswoman for Vodafone Hutchison Australia told iTnews that the carrier will make a statement shortly.
Telstra's director of network and commercial planning, Anthony Goonan, said the project was "many years" in the making and had been given the go-ahead late last year by NSW Transport Minister Gladys Berejiklian.
The state's Premier Barry O'Farrell said on Twitter that it was "great to see [Berejiklian] improving wifi coverage on CityRail services".