Yes, this is correct Openreach have announced they will be switching off their existing PSTN and ISDN network by 2025. The existing network/exchange is now very old and requires a high level of maintenance.
There are many telephone systems that are built on ISDN and analogue lines and therefore these systems will require change, updating (if possible) or require new systems.
Our advice is not to worry and be pressured into purchasing new technology that may not be fit for your business. Give us a call so we can review your current telephony operations and can advise on the specific impacts this will make to you.
By discussing this as early as possible and in plenty of time gives you the information and financial implications so you can plan ahead.