BT Digital Voice is BT's replacement to the Public Switched Telephone Network (PSTN) which will complete by 2025
Whether you are offered BT Digital Voice will depend on what Telephone Exchange you are on historically, the capability of your broadband and the capacity of the new BT Digital voice investment. It will start during 2020 and then ramp up to 2024.
Previously VoIP phones were directly dependant on an IP interface but BT has included an Analogue Telephone Adaptor (ATA) in their latest hubs ready. This means you can plug a traditional corded phone directly into the Hub/Router or in fact connect all your existing phones via existing home wiring. The hub needs to be set up with the relevant VoIP/VoBB credentials to connect to the new service. Your existing number will be able to be transferred.
BT will of course try to up-sell you new devices and it is in their interests to get you to discard old telephone wiring which in many homes causes no end of issues. You can plug in existing DECT phones or cordless products.
Until you get invited to join BT Digital Voice then if you retain a fixed landline you will be connected by one of the following methods:
a) Copper pair from your house to the local exchange (ADSL and "Fibre" FTTC) via your BT main phone socket (NTE)
b) Fibre Voice Access via the Telephone socket on the Optical Network Terminal (ONT) (used on current Full Fibre FTTP installs)
As BT transitions from their PSTN then other ISPs will also start to offer Broadband without a land line (will include ADSL and FTTC) and will offer instead VoIP. Either they will provide a Router with a ATA in it or a separate ATA you can plug in. But beware not all VoIP is the same. Traditional "Telco" providers such as BT will ensure that the voice quality and prioritisation of the phone call (data) will be maintained. So be careful which provider you select going forward.
Going forward there will be combined mobile and VoBB products and services.
