The world's richest man says he believes the cost of connecting Australia's national fibre optic broadband network may be too high.

Carlos Slim Helu, who has owned Mexico's national telephone company since its privatisation in the 1990s, is in Sydney for the Forbes global CEO conference.

He says the connection estimate of $7,000 a home for the NBN is too much and not necessary because of constantly changing technology.

"Because technology is changing every time, I think to connect - I don't know how many houses we're talking here but maybe six million houses, seven million houses - $7,000 per house is too much," he said.

Mr Slim says the high-speed broadband plan should also focus on wireless technology, not just optical fibre, to connect homes and workplaces.

"You need to have in this multi-platform [a bit] of everything - mobile, landline, fibre, cable and copper," he said.

"I think fibre is not enough - you need to have a good network of wireless that you can connect it with in thousands of places with a wi-fi service."

Mr Slim says fibre should be the backbone of the network but in rings near homes and businesses to allow a variety of broadband connections.

Mr Slim also has interests in infrastructure, property, oil and gas.

The son of Lebanese migrants, Mr Slim is one of the largest shareholders in the New York Times company that owns the prestigious US newspaper.

According to Forbes Magazine, he is worth $US55 billion, more than North American billionaires Bill Gates and Warren Buffet.

The Forbes conference named him as a hero of entrepreneurial capitalism.

But the first Mexican to top the world's rich list played down his wealth.

"The important issue for success in life is to have a complete life environment," he said.

"It is not a money issue or a material issue, but it's that all your environment, you're family, your friends, your personal life, your time to know to appreciate the colours, the sunset, the flowers, the weather the places, the people."

Delving briefly into Australian domestic politics, Mr Slim says he believes a tax on carbon is essential.

"I think it's important a carbon tax, and maybe the way to make it more easy is to have the carbon tax and that the big part of the tax be used in the country that generates the carbon tax.

"Some countries don't support that because they will give money to others."