Australian telco, Telstra has warned that its $11 billion deal with Labor's National Broadband Network (NBN) company could come unstuck.

The telco said the deal could come apart if it was forced to maintain its ageing copper network for those who do not want to connect to the fibre network.

Under the non-binding agreement, Telstra would get $9 billion to transfer its traffic on to the NBN and to gradually shut down its copper network with customers moving to the new fibre network.

However, fresh concerns over the sluggish NBN take-up rates in Tasmania, coupled with the ineffective methods being used by state governments to connect the new fibre cable to premises, could end up seeing large parts of Telstra's copper network in use beyond the its use-by date and in parallel with the new NBN.

Telstra chief executive, David Thodey, yesterday exposed the fragility of the agreement, a deal which according to industry experts underpins the ambitious NBN project's success.

Thodey said the commercial terms had to be such that Telstra was not left to maintain the copper in that period, otherwise the value would be destroyed. He added that it had to be done in commercial terms and that was the reason why it was the governments' prerogative to decide how to incentivise people to migrate to the new network.

According to analysts, Telstra spends $300 million a year in capital expenditure on its copper network and as much as $1billion a year in operating costs to maintain its asset that has an extensive reach. It was expected the vast majority of its customers would migrate to the NBN, but even if a fraction remained on the copper network, the maintenance costs would be too high.

Under the terms of the $11billion deal, Telstra is supposed to be relieved by the government of its universal-service obligation to provide a fixed-line service to premises, however, it was not clear if that provision would be extended to premises within the NBN's fibre footprint.

According to a spokeswoman for communications minister Stephen Conroy, no decision had yet been made in relation to switching off Telstra's copper or cable networks, but she said the NBN Co would not carry the burden of maintaining the copper network.

The NBN Co has eight years to connect 93 per cent of the nation, but given the sluggish rate of activations in Tasmania -- about 50 per cent this target woyuld be difficult to achieve, according to indications. This week, the Tasmanian government announced it would introduce laws to allow homes and businesses to be automatically connected to the NBN unless they refused in writing.

New South Wales and Victoria have refused to consider Tasmania's lead and adopt an opt-out system which has led to fears that the first mainland sites could be subject to the same lowly take-up numbers.

Meanwhile, Thodey has played down concerns that the take-up of the National Broadband Network (NBN) had been slow.

He said it was so hard to get all the parameters right. He added that when putting a service to a home one had to get it connected, one had to get the pricing right.

He said that all of Telstra's experience of the introduction of new technology suggested that it took a long time to get established and then once it took off it took off.

Thodey was speaking at a business function in Sydney.