The countdown is on for more than 11,000 NSW homes and businesses that are less than a week away from NBN "D-Day", when their copper phones lines will be disconnected for the compulsory migration to the national broadband network.

On April 17 around 11,300 homes and businesses across Rookwood, Lidcombe, Jamisontown, Windsor, South Windsor, Bligh Park and Sawtell near Coffs Harbour will reach the copper disconnection deadline.

Work to build the National Broadband Network is expected to be under way or complete by September 2016. Credit:Henry Zwartz

Residents and business owners who have not placed an order for an NBN service by this date will have their phone lines running flat within 10 business days.

"The important thing is to get your order in before the switch off date. If you don't then you will be on a list to have your services disconnected. However, if you wake up on the 18th, you can still call your telco and put an order in to try and have your services reconnected (or connected) but there may be a time lapse," NBN Co spokesperson Dan Chamberlain said.