ALMOST 10 million households will have to sign up to the national broadband network to keep their landline connections, after the government clinched two critical agreements that raise the cost of unravelling the $36 billion project.

Under the deal announced yesterday, taxpayers will pay Telstra $11 billion to shut down its ageing copper wire network over the next decade and transfer these customers to the network.

Everyone will have a choice ... Communications Minister Stephen Conroy stressed households will not have to pay to connect to the NBN.

The country's second-biggest telecom firm, Optus, will receive up to $800 million from the government for dismantling its cable network and moving 500,000 people to the network.

Both deals support the business case for the nation's biggest infrastructure project, and give the NBN a stranglehold in fixed-line telecommunications.