Since a voip over FTTC is not a standard product from Openreach then its not going to happen until the product teams get to work, and providers agree on what they want from it. None standard CPE (wires only) make it harder for VDSL2, than GEA-FTTP where FVA makes use of the Openreach ONT. SoGEA may well bring this for VDSL2 but its still an on the way thing, with no clear indication of any retailer keen.
Which retailer is the phone service these people trying to order via?
Phone numbers are already a virtual element, so if a pool runs out locally then a code from elsewhere can be used, maybe the neighbours wanted to insist on a specific area code (there was some Bath local press with people complaining about not getting the prestigious local code they thought they would)