Rolling fibre out to the bush could cost up to $10 billion, almost as much as laying the cables across every Australian capital, according to Telstra.

The provision of broadband to regional areas is a hot topic between government and proponents vying for the National Broadband Network (NBN), due to the cost of linking dispersed populations with expensive fibre cables.

Under the government's NBN election pledge, fibre must be deployed to 98 percent of Australians, however it does not exclude network proposals that utilise a mix of telecommunications technologies.

Speaking on Telstra's $25 billion costing of the NBN, spokesman Jeremy Mitchell said supply of fibre to regional areas would account for the final $15 to $25 billion portion.

"Our estimated price range depends on what you do in regional areas; our initial plan covering Australia's five largest cities cost $5 billion," Mitchell said.

"The costs rise dramatically in the cities and that last $15 to $25 billion really determines what you can do in those areas."

"Our costing model allows competitors to work out the cost per metre of digging a trench for cables, fibre, and other equipment. It includes all infrastructure details to access and build networks to replicate our own."

While Mitchell wouldn't be drawn on whether regional Australia would be best served by ADSL2+ and wireless technologies, he said Telstra had activated over 200 DSLAMs for high speed DSL access.

Fixed broadband deployments such ADSL2+ in regional areas will be expensive, primarily because premises must be within 1.5 kilometres of the enabled exchange, and up to 2 kilometres for communities with new thicker copper lines.

The statements follow claims by Optus that it could build the NBN for $12 billion with a 12 percent Return of Investment (ROI).

Mitchell took the opportunity to attack the telco, arguing it should re-evaluate it's claims in light of the Optus network cut which disabled phone, mobile and Internet connections for one million Queensland customers.

Responding to a government request for submissions on how the NBN can serve regional Australia, Telstra took a backflip on its much-touted customer-pays funding model for building infrastructure in isolated areas, arguing government and commercial organisations wanting access to the fibre should chip in for infrastructure costs.

"Telstra generally supports a customer subsidy-base funding model where government wants to improve access to communications for particular groups ... a direct funding model is more appropriate for [isolated areas]," the statement read.

The company claimed in the document that ADSL technology is available to 92 percent of Australia, and ADSL2+ is accessible by 79 percent.