That article is still somewhat vague, especially as so many homes will continue to be connected by a copper wire connection as "Fibre-To-The-Cabinet" (FTTC) as that's the sole means of getting broadband for those homes.
That is not a problem in that VoIP [ the underlying technology for digital voice calls] works over copper, or aluminium, we have been doing so at home land line for years. In our case originally via Skype more recently Sipgate.
The requirement is simply for a broadband connection, not the medium it is transmitted on, indeed we use it either on our landline or on our mobiles, the latter for making very cheap international calls.
Those presently without broadband, a claimed just 2%, are going to "looked after" by an abridged broadband connection, that only services a voice line. I understand Ofcom requires that a non costed facility the line providers have to provide. It will require I understand the additional running cost of a mains connection to power that device.
I really do believe a very small percentage of the population will be impacted, most as I do will be able to use their existing handset, just plug it into a router or other adaptor that the Openzone etc wall socket.
Whether the more savvy keep with BT or their other landline providers for their VoIP service is quite a different matter. For us, with a high international call requirement, cost wise it was a no brainer to use non phone line providers, much like many now use just mobiles for UK voice calls.
Apart from getting a letter, and a device to duly plug in, I am thinking that will be the extent of most people's awareness that anything has changed. The improved quality could well be the only thing we sense, if my Sipgate VoIP service is anything to go by!
For a long while, VoIP itself has been how your landline calls have travelled, one getting away each end from the exchange