Slim also said fibre was not enough and the government should invest in mobile, wireless, cable and copper networks as well. Stephen Conroy makes his announcement. Credit:Glen McCurtayne In response, Conroy's spokeswoman said it was clear Slim had not read the government's NBN implementation study. It would be forwarded to him. "Mr Slim's comments about the NBN are no surprise, given he has become the world's richest man by owning a vertically-integrated monopoly," Conroy's spokesman said. The government said the implementation study and experts agreed that fibre-to-the-home was the optimal future-proof technology with a lifespan of 30-50 years, and wireless would never be capable of matching the capacity of fibre.

Conroy said the study found that the $43 billion cost of the network was a conservative estimate and there were opportunities to reduce the cost significantly. Mexican tycoon Carlos Slim Helu holds a press conference at the Forbes Global CEO conference in Sydney. The NBN would generate sufficient earnings by the end of year seven so that the investment required by the government would peak at $26 billion, of which $18.3 billion would be required over the next four years. "The implementation study confirms that the NBN Co can develop a strong and viable business case, generating stable and positive cash flows, and that the government will get a moderate return on its investment sufficient to cover its cost of funds," the spokeswoman said. On Lateline last night, opposition communications spokesman Malcolm Turnbull continued to attack Conroy over the cost of building the NBN and the lack of a cost/benefit analysis.

He said billions of dollars should not be wasted on laying fibre-to-the-home when it was possible to build the existing network and add wireless support for the regions. "I'm not interested in demolishing the NBN," he said. "I'm interested in exposing the hollowness of the government's justification for the NBN and that, I suppose, will demolish their shabby and empty argument." Conroy responded by saying the investment in the NBN, $26-$27 billion of which would be contributed by taxpayers and the rest by the private sector, should be looked at over the 40-year life of the network. He said it was essential infrastructure for the nation's future and the existing networks would not support the kind of applications that will be required.

"You cannot have high-definition video conference, you can't do remote diagnosis, you can't send big files ... [existing networks] cannot deliver the sort of broadband capacity that we're going to need to move into the new services that are yet to be invented and the existing services that are available today, and Malcolm Turnbull knows better," Conroy said. Conroy has said he is considering the Greens' request to keep the NBN in public hands after it is built, as opposed to the original plan to sell it to the private sector after a number of years. Turnbull said it would just create another government monopoly. Loading "This monopoly is so repugnant to the provisions, the competition laws of the Trade Practices Act, it could never get approved by the ... ACCC," he said.

"So Senator Conroy has to pass special legislation to effectively take it out of the competition laws in the Trade Practices Act. This is a remarkable act of government - you know, of direct government intervention."