From Vodafone Website:
Any extra telephone sockets in your home won't work after you switch to Digital Voice. You'll need to plug all phones into the back of the router or use wireless phones that work with Digital Voice.
(Link to above information: https://support.vodafone.co.uk/Broadband/Pro-Broadband/1751006322/What-is-Digital-Voice.htm if allowed in context.)
That suggests to me that if you can plug a phone into the back of the router, then you can plug existing phone extensions into the back of the router in the exact same was as you can with BT Smart Hub 2.
The reason they don't 'tell' people that is because it muddies the waters — too much information confuses people, so they just tell you 'won't work' instead of 'with a little work and knowledge, it will all work just as it ever did'.
FWIW - thanks to advice on this forum, I fitted a double ended BT 431 to the green port on the SH2 (FTTP) - corded 'phone plugged into one outlet and the other to a nearby extension socket - so that other sockets are live as previously. Disconnected the redundant copper cable, replaced the old Master (rusted connectors) with a new socket.
Very pleased with the FTTP - speed as advertised and no drop-outs. All well and good so far!
its only BT that has arranged for a pseudo-analogue phone socket to be on their SmartHub 2. You can plug your original phone into this, or you can plug your extension wiring into this, or you can get DV adapters, plug them into any mains electricity outlet you like and plug phones into these. So you can have phones wherever you want them in your house.
Vodafone VOIP phones do not provide any of this functionality and never have done.
Note the two green sockets on the current Vodafone router.