VoIP services rely on mains power and will not work in a power cut. Ofcom has issued guidance on how telecoms companies can fulfil their regulatory obligation to ensure that VoIP customers have access to the emergency services in such circumstances.
When your time comes to move to VoIP services, if you are reliant on your landline, you should discuss your situation and needs for a back-up solution with your service provider before you are moved over.
Ensure that the equipment you have has a decent battery back-up in the event of a power cut. If you are a vulnerable person and you rely on your landline for medical or other reasons, your service provider should provide you with equipment which has a suitable back up.
It is important, when the time comes to switch from analogue to IP, that you have made your provider aware of any special needs in this respect.
View Ofcom’s full guidance for further information: