Yes, fair point. She does have a mobile but prefers the landline. My thinking was if she has to change eventually she might as well get a free phone but as you say, they are cheap enough.
Interesting that phones will no longer work in a power cut.
Digital Voice is delivered to the BT Smart Hub 2 over the Internet. If power is lost to the hub, then none of the phones will work. Any other equipment like alarms that rely on the phone connection, will also stop working.
Also, the free DV phones still need power to charge up the battery, so if they go flat, then they do not work.
BT do sell a suitable backup power supply for the home hub, but its not cheap, and other alternatives are available.
@tmarsh12345 if your Mum is vulnerable and moves to digital voice she would be entitled to a free battery backup unit to call the emergency services if needed. However, as you mentioned she has a Mobile so that could be used in the event of a power cut.
You need to be realistic as to how long a mains UPS will last in a power outage, smaller ones are lucky to get 30 mins.
OFCOM recommend an hour minimum for the hub at least……remember your handsets are battery powered and likely to last hours without power and they are connected to the hub not a DECT base that would have required power to work. So you only need to power the hub really.