The liberalisation of equipment supply in the early 1980’s ( so well over 40 years ago ) requires that the customers own extension wiring be connected to the removable consumer panel of the master socket , so if a customer made a mess of their own wiring , it’s simplicity itself to disconnect it from the ‘line’ by unplugging the consumer panel from the master socket , call out Openreach in these circumstances where the customer messes up and refuses to disconnect their wiring by removing the panel and insisting on a visit is a chargable event ….messing internal wiring up only afects that consumers line , no one else’s , so in that respect OR don’t particularly care .
As far as does voice reinjection need to be from the master socket , no , any socket in the ‘chain’ can be utilised to connect to the router but the isolation between the ‘outside line’ and the internal wiring needs to be at the master socket , plus as stated if the router isn’t to connect to the master socket but an extension socket then a DSL connection needs to remain between the master and extension socket for the router to be able to use that extension socket .
I’m not judging , if someone wants to stand in a hallway to make or receive calls , that’s entirely up to them , but in your case the obvious and simple solution is a DECT handset running on its battery during the day , located in the hallway , and placed on its charging cradle to charge overnight , that charging cradle likely to be the DECT basestation that’s connected to the router phone port …that way no mains needed in the hallway , what’s more should the person on the phone fancy a comfortable sit down somewhere else , they are not tied by a phone cord , although I sense a ‘why should I buy a new cordless phone’ comment will be forthcoming.
