Commuters will start receiving phone and internet coverage in some of Sydney's train tunnels this week - 16 years after Optus first offered to carry out the work.

The telco is laying 10km of cabling on the North Shore and Western lines so that mobile, laptop and tablet users no longer suffer regular network drop-outs.

But it's been a long time coming.

NSW Transport Minister Gladys Berejiklian said Optus first approached the state government in 1996 offering to do the work.

She blamed the previous Labor administration for failing to take up the offer: "It is ridiculous it has taken this long.