BT Digital Voice (DV)

The impartial information on this page is given free of charge and without prejudice
It is accurate at the time of writing and may change over time - always check with BT or your provider

BT Digital Voice
An overview

This page only deals with BT Digital Voice but some of the information is applicable to other telecoms providers.  BT intend to roll out Digital Voice to the whole of the UK by 2025.

Most of the UK Telephony providers are converting their networks so they have no copper connectivity directly connected to their exchanges.  But copper wires will still exist in many places, mainly from the house to the green street cabinets.

This does not mean that the copper wires to the premises will not be used.  If you do not have fibre to the premises then the existing copper wires will still be used to provide the service, but these copper wires will not connect to the exchange like they used to.  The copper wires will be interfaced by fibre at a green cabinet and the fibre will then be fed into the BT IP network.  BT and other similar providers did this to reduce the cost of replacing the local exchanges and instead chose just to route data traffic to remote switching centres.

Please beware, because the customer is now lumbered with having to power all the equipment in their home, that in the event of a power outage no 999 or 112 emergency services will be available.  Ofcom have stipulated that those who are vulnerable and have emergency call devices should be supplied with a 1 hour battery backup, free of charge.  BT will try to charge for these devices so fight your case and complain to Ofcom if BT refuse to supply one.  If you have no mobile service in your home then your supplier should provide a resilient service.  Please contact your supplier about this.

Another point to remember is that if you have specialist devices connected to your line, like burglar alarms or emergency call buttons, then you must contact your supplier to advise you are moving to the new Digital service.  Not all these devices will work and only your supplier will know what to advise.

No matter if you are on fibre, broadband or just have a telephone line only, you will be provided with a hub/router from BT or your service provider.  These have an integral telephone socket which will provide dial tone.  This socket will allow only Tone (MF) dialling and will not support a dial telephone.  Click here if you have a dial telephone.

Your original master socket will either be made redundant (if fibre to the premises) or will connect to the hub only (non-fibre to the premises users).

BT will now retain ownership of the Smart Hub they provide.  If you move to another provider then the BT Hub will have to be returned to BT, but it also means that if the hub goes faulty then BT have the responsibility of replacing it free of charge.

The system will provide you with two exchange lines, albeit on the same number.  This means that two people can dial out at the same time or receive two incoming calls at the same time, but only two calls in total.

Because you have two lines, the Call Waiting function is pre-enabled.  Call Waiting tells you when other callers are trying to get through, whilst you are on the line. You'll hear a discreet beep when someone is trying to get through to you while you're on the phone. You can choose whether or not to take the call.  On most DECT handsets the R button can be used to answer the second call.  To deactivate this function you will have to call BT or manage it via your BT online account by logging in and then click on My BT - Your Products - Digital Voice - Call Waiting.  It is a zero cost option.

Another major change for users is that you have to include the national area dialling code for ALL outgoing calls, including local calls. 

Please be aware that Voicemail is pre-enabled for Digital Voice customers.  If you still wish to use your original answering machine then you must disable the Digital Voice voicemail.  There are two ways to do this.  Call BT and ask them to cease the Voicemail or login to your BT online account.  The account option is best as the voice is removed straight away.  Login and then click on My BT - Your products - Digital Voice - Voicemail essentials.  It is a zero cost option.

Click for Frequently Asked Question's

Fault finding on Digital Voice

SIP connectivity (Asterisk)

Types of service and connectivity

Telephone Line only
A BT Smart Hub 2 or similar will be provided by your provider.  This will have a standard BT socket on it so a standard telephone will still work (but only if it is a tone (MF) dialling phone).  The hub will be locked to telephone line use only.  It is mains powered and requires a mains socket nearby.  The telephone socket in the hub can be connected to your existing house telephone wiring - click here for details.

BT will also provide a Digital Voice Adapter (free of charge) which will allow the phone to be placed in another position within your premises.  This adapter requires a mains socket.

BT will supply a cordless phone that connects to the hub, if requested.

Broadband/Fibre to the Cabinet (FTTC) and Telephone line
A BT Smart Hub 2 or similar is fitted which has the same functionality as the Fibre to the Premises hub described below.  The difference is that it is connected via broadband and therefore operates at a lower speed.  It also uses the local copper cable from the green cabinet, which is not as efficient as fibre to the premises.  Even though you may have Fibre to the Cabinet, the local connection will be completed with copper.

The original Master socket will still be used but will provide Broadband only and the cable that connects from the Master socket to the Broadband socket on a Smart Hub 2 is non-standard, as it has a non-standard RJ45 connector on the hub.  The telephone line is now presented on the rear of the hub and is MF (tone) dialling only.  This socket can be connected to your existing house telephone wiring if required - click here for details.

The hub is mains powered and requires a mains socket nearby. 

BT will also provide a Digital Voice Adapter (free of charge) which will allow the phone to be placed in another position within your premises.  This adapter requires a mains socket.

BT will supply a cordless phone that connects to the hub, if requested.  They will supply up to two, free of charge.

Click here for a pictorial overview


Fibre to the Premises (FTTP) and Telephone line
A BT Smart Hub 2 or similar is installed that is a:-

  • Router

  • WIFI device

  • Analogue telephone line connection

  • DECT wireless device

The BT equipment supplied at a fibre to the premises installation require 2 mains power outlets.

The BT Smart Hub has 4 network ports (RJ45) and a telephone socket.  The telephone socket can be connected to your existing house telephone wiring - click here for details.  This socket will allow only Tone (MF) dialling - and will not support a dial telephone.  Click here if you have a dial telephone.

BT will, if asked, supply an Digital Voice analogue adapter and a Digital Voice telephone or two Digital Voice telephones.  The digital adapter allows an analogue telephone to be connected at a remote location.  The adapter is DECT based and requires a mains socket.  This adaptor will only support Tone (MF) dialling- and will not allow a dial telephone to dial out.  Click here if you have a dial telephone.

The Digital Voice telephones supplied by BT are cordless DECT telephones.

Click here for more information on how to use DECT with the Smart Hub

Click here for a pictorial overview

Technical Information

Wiring the Hub telephone socket to house wiring
Your existing house wiring (if you have more than one socket in the premises) will be connected to the NTP socket i.e. the first one, which is called a master socket.  This socket is owned by the provider and will have a removable plate on the front.  Your house wiring connects to this removable plate.  As this wiring will not be connected to the new hub it has been made redundant.  But it can be connected to the back of the hub if required.

If you wish to connect your house wiring to the hub then the house wiring MUST be disconnected at this master socket.  This is essential and if you do not feel confident about this then call an expertDo not just plug a cable into the front socket on the Master Socket and the other end into the telephone socket on the Smart Hub!

You will require a secondary telephone socket (Line Jack Unit No. 2/3A is best) and a new line cord with a plug at both ends, which can be purchased from many places.  Most sockets require a special wire inserter tool but a company called Kenable can supply a master Line Jack Unit No. 2/4A (code no. 004629) socket which has screw terminals - but this will require the yellow, blue and stripped components removing with a pair of cutters.  A line cord must also be purchased which has two BT style plugs at each end.  The original broadband filters must still be retained at each telephone connected to the house wiring.

Make sure that you have dial tone on the Smart Hub telephone socket.  Fix your new socket next to the NTE.  Remove the front plate from the existing master socket (NTE).  Disconnect the house cable from the front plate making a note of which colour wires are connected to which terminals - they are numbered.  Pull the house cable out of the original NTE socket and connect to your new master socket ensuring that the same wire colours are connected to the correct terminals.  Then use the new line cord to connect from the hub to the newly installed socket.  All your sockets should now have dial tone.

Please note that the Smart Hub may not have enough power to ring all your telephones in which case switch some of the ringers to Off.

DECT on the BT Smart Hub 2
This hub supports DECT (CATiq 2.1) and has two internal DECT antennae.

A maximum of five DECT cordless devices can be connected to the hub.  Click here for the BT statement - at the end of the video

Numerous DECT devices can be connected to the hub including other makes of DECT telephone.  The PIN  is 0000.

An important point to remember is that DECT is similar to WiFi in so much as it has a range which can change depending on the building.  In some cases no signal may reach your phone and the only way to remedy this would be to use a DECT repeater device.  BT have advised that the Smart Hub 2 does NOT support DECT repeaters (Feb 2022).  Click here for a work around

To see the DECT phones connected, log into the BT Smart Hub 2 Manager (the login information is on the rear of the hub).  Navigate to the Phone section, which is found to the left of the home page.


BT Digital Voice Adapter
This is a DECT device which has a BT socket on it.  This allows a standard telephone or bell to work remotely in locations away from the hub.  It has a good ringing output which is thought to be REN 3.  It will allow only Tone (MF) dialling - and will not support a dial telephone.  Click here if you have a dial telephone.  One of these will be required if an extension bell is installed or you wish to locate your phone away from the hub.  A Digital Voice Adapter will use up one of the 5 DECT device registrations available on a BT Smart Hub 2.

Linking to the hub:-

  • Plug the Digital Voice Adapter into a mains socket and switch on.

  • Press the WPS button the side of the hub.

  • Within 1 minute of pressing the WPS button, press and hold for 6 seconds, the small button found on the right hand side of the Digital Voice Adapter.

  • Once registered the Digital Voice Adapter will show a green light on the front.

Click here for the User Guide


Phones that work with Dials or early keypads
Many people have antique telephones with dials or an early press button telephone (with no * or # buttons) but because the Smart Hub 2 and Digital Voice Adapters will only operate with tone (MF) dialling, then use of a dial is ineffective.

So what to do - you need to purchase a Dial Pulse to MF converter.  These converters can be used in a number of ways:-

  • The converter is plugged into the BT socket on the hub and a dial phone connected to the converter.

  • The converter is connected to a Digital Voice Adapter and a dial phone connected to the converter.

  • If your house wiring is connected to the hub then the converter can be plugged into a socket and a dial phone connected to the converter.

There are a number of converters to be found, but be careful as some of these require special wiring into the phone or need a power supply.

It is better to buy a self contained converter and there is one called the Dial-A-Tone.  This dialler will convert the dial pulses produced by the phone into tones, which will be recognised by the new equipment and does not require a power supply.  This sort is available from a company called Vintage Telephony.  This link takes you directly to the Dial-A-Tone page  This web site has no connection with this company.


BT Digital Voice Handsets
There are two types of handsets (as of October 2021) and these are called Essential and Advanced.  See below for the specification.

These handsets are powered by batteries and are supplied with a charger which requires connection to a mains socket.

With a new telephone pull out the plastic tab on the base of the telephone to engage the batteries.  Then plug the charger into a mains socket and then place the phone in the charger.  Leave on charge initially for a minimum of 16 hours.

Linking new phones to the hub:-

  • On the phone press OK

  • The display says "register this handset to the hub"

  • Press the WPS button, on the side on the hub, for 2 seconds - The WPS button flashes blue whilst registering.

  • The phone will say registering and when it is registered the display states "Registered"

For more information on these phones please visit the BT web site.

Click here for the User Guide

BT guide on how to register a DECT phone

Overview of both DV Telephones

  Advanced Digital Phone with Alexa Essential Digital Phone


Display: 2.0-inch colour display 1.8-inch black and white display
Alexa Button: Yes No
Handset Features
HD Calling: Yes Yes
Phone Book: Yes, up to 500 saved numbers Yes, up to 500 saved numbers
Hands-Free Calling: Yes Yes
Caller Display: Yes Yes
Call Waiting Indicator: Yes Yes
Voicemail Button: Yes Yes
One-Touch Calling: Yes, using Alexa button No
Accessibility Options: Yes, includes:
Ringer Volume Boost
Large Text
Other: Control smart home devices
Check news & weather
Stream music (using Alexa)
Handset Connectivity
Cordless: Yes (uses DECT) Yes (uses DECT)
Wireless Range: Up to 50m indoors
Up to 300m outdoors
Up to 50m indoors
Up to 300m outdoors
Requires Smart Hub 2: Yes Yes
Battery Life: Up to 12h talktime
Up to 180h standby
Up to 12h talktime
Up to 240h standby
Handset Dimensions: 19.1 x 5.1 x 3.9 cm 19.1 x 5.1 x 3.8 cm
Charger Dimensions: 2.7 x 7.3 x 7.2 cm 4.2 x 8.0 x 7.6cm
Weight: 151g handset, 67g charger 151g handset, 67g charger


Frequently asked questions

Q.  I have a bell in my house. Will it still work?
A.  If it is connected to a Digital Voice Adapter, the back of the hub or the house wiring (if this is connected to the hub).

Q.  I have a dial phone.  Will that work on the new system?
A.  The new system only works with tone (MF) telephones.  If your telephone is press button then see if there is a switch on the base to change the way it dials out (marked LD or Pulse or MF).  Choose MF if it available.  You can also buy devices that convert dial pulse to tone, so antique phones can still work.  Click here for more information

Q.  I have my telephone line from BT and my broadband from another company.  How will that work?
A.  Either use BT as the telephone and broadband supplier, or use your original broadband supplier and get an internet based telephone provider to supply the line.  Internet telephone providers use a VOIP service which comes in different flavours.  Speak to your broadband supplier or search the internet for "VOIP residential suppliers" in the first place.

Q.  If I use a VOIP telephone service can I still use my old phones?
A.  You can, if the VOIP provider can connect to a device called an Analogue Telephone Adapter (ATA).  ATA devices have a telephone socket and a network port that will connect directly into one of the network ports on the rear of the Smart Hub.  Some providers will sell you an adapter or you can buy your own.  These devices require programming and your supplier will advise of the settings.

Q. Can SIP devices be connected to a BT Smart Hub
A. The answer is yes but you will have to make sure you have information on connectivity to hand from your SIP provider.  Click here for Asterisk server connection.  If you have other SIP device information then I will publish it to help others.

Q.  How many DECT wireless telephones can I connect to the Smart Hub 2?
A.  BT advise that up to 5 phones can be connected, but remember that a DV Adapter will use up one registration (if fitted).

Q. My wireless DECT phones do not work in certain parts of my house - can they coverage be extended?
A.  Normally a DECT repeater device could be used but the Smart Hub 2 does NOT support these devices.  There are a couple of ways to get around this:-

1. A DV adapter could be installed at a point away from the Smart Hub 2 and then connect a DECT telephone base unit into the DV adapter.  The DECT base would operate separately from the DECT on the Smart Hub 2 and would not have the same functionality as phones off the Smart Hub 2, but will receive and make calls.

2.  Connect a DECT base unit (that supports DECT Repeaters) into the socket on the Smart Hub 2 and then fit a DECT repeater at a distant point and register it to this DECT Base unit.  You will not get full interoperability with the Smart Hub 2 but will be able to answer calls, receive calls and transfer calls to any DECT telephones connected to this stand alone DECT system.

Q.  Do I have to use BT supplied telephones?
A.  No - but the BT phones will offer total functionality.  You can use your original telephones either via a Digital Voice Adapter, the socket on the back of the hub or your house wiring.  Other makes of Cordless DECT based telephones can also be registered to the hub, but they will not provide for complete functionality.  If you have DECT wireless phones already then you can just plug the main base unit into the back of the BT hub and still use them.

Q.  What about answering machines?
A.  You can use your own answering machine.  The BT Hub does not have an internal answer phone but BT provide the answer service at the exchange.  If you use your own answering machine then the BT answer service must be deactivated.  The BT answer service is always activated on change over - so be aware.

Q  People complain that they leave voicemails and that I do not reply to them.
A.  The BT Voicemail is most probably switched on and this is answering your calls before your answering machine cuts in.  Get the BT Voicemail disabled.

Q.  My WiFi does not go very far?
A.  Probably due to the building it is installed in.  BT can supply WiFi extenders to help extend the distance.  Each extender requires a mains socket.

Q.  I use my old DECT wireless system and phones and cannot see the calling number.
A.  This happens sometimes.  Make sure that CLI is activated on BT.  Then check your DECT system to see if the caller log or missed call log shows numbers.  If you can see numbers then add these to the internal directory of the DECT system and name them.  The name should then show on incoming calls.

Q.  I have an phone which has stopped working - what do I do?
A.  Does the internet work - try to reach  If the internet works then use a known working telephone and plug it into the back of the Smart Hub.  If you still have no dial tone then call BT or your provider.

Q.  The white BT wall box (ONT - Optical Network Termination Device) that connects to my Smart Hub has a red light showing stating a fault - why is this as the phone and internet work fine?
A.  This normally happens after a power failure.  Inside the ONT are a couple of batteries.  These batteries will be at a low voltage after a power outage and will start recharging.  As they charge the red light will extinguish and the charging light will go yellow and then go out when they are fully charged.  Wait 24 hours and if the red light still shows then the batteries will require replacing.  This is the customers responsibility according to BT.

1+1 ONT

The battery pack is shown to the top right of the picture with the ONT on the top left.  The ONT cover consists of two parts which are hinged on the left.  The bottom cover opens by just pulling on the right hand side side.

Before working on the battery unit ensure that the power is switched off and that the battery lead is removed from the ONT.

The top cover is fixed by a single Philips screw which will now be visible.  It is to the right and just under the top door - you can see the screw hole in the picture.  With the screw removed the cover will require a good pull to open.

With the both covers open, the battery unit can be seen to the right.  To remove the battery pack, slide the battery unit upwards and lift off the locators.  On the rear of the battery box is a slide cover, which once removed exposes the four AA batteries.  Unsure they are replaced with the same rechargeable type.  Do NOT, under any circumstances, use ordinary AA batteries.

Some older units will have an external battery box (before April 2019).

An alternative to replacing batteries is to remove the Battery pack in its entirety and plug the power cable directly into the ONT.  This is not advisable as batteries do provide some form of mains filtering.

BT advise that the battery backup unit uses four 2000 mAH-NiMH BYD rechargeable AA batteries at 1.2V.

This YouTube video shows how



BACK Home page BT/GPO Telephones Search the Site Glossary of Telecom Terminology Quick Find All Telephone Systems

Last revised: June 07, 2022