This will not happen immediately so please don’t panic if you are currently using traditional landlines.
Openreach has announced that it will withdraw its sales of the old-style lines by 2023 so there’s plenty of time to upgrade by the deadline of 2025. If you were considering moving into new offices soon, it would make sense to go for the new VoIP option but if you are staying put there is no need to make the switch immediately, your PSTN lines are good for a few years yet.
Now would be a great time to do a little audit. Make sure you know what type of lines you have so you are prepared for the changes when they happen.
Here is a link to Ofcom’s Policy Positioning Statement on the Future of Fixed Telephone Services.