An upgrade of landlines to digital technology has begun in Northern Ireland.
It is part of BT's Digital Voice project to replace analogue phone lines with digital ones.
BT has described the project, which began in parts of England in July and August, as a "once-in-a-generation" undertaking.
Customers in Northern Ireland will be contacted at least four weeks in advance of the switch.
The upgrade will see BT and many other telecoms operators in the UK provide services over a broadband line.
BT said the work was "essential" as it would replace technology that was fast becoming obsolete.
The company said that landline phones were not being phased out and, for the majority of customers, the switch only involved plugging the landline phone into a broadband router instead of into a wall-mounted socket.
BT said for almost all customers Digital Voice will have no impact on how they use their home phone.
Vicky Hicks, senior engagement manager at BT, said the benefits of the switch include advanced scam-call filtering capabilities and clearer call audio.
"For almost everyone, moving to Digital Voice will be a simple and free transition with no home installation work required," she said.
"If you feel you need additional support with the transition, or you think you are vulnerable, please do tell us."
Certain customers will not be proactively switched initially, including those with a healthcare pendant, those who only use landline, those with no mobile signal, and also those who have disclosed any additional needs.
As part of an awareness campaign, BT will be facilitating a series of town hall events and pop-up stands across Northern Ireland in the coming weeks.