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Caller Display


Are some standalone caller display battery powered units not compatible with the new hub landline phone service ?

Mine has stopped working and now seems to be blocking all calls from going through it to the phone. It is a very old BT Caller Display 20. If I remove the batteries in the display unit the calls are not blocked and the phone works normally.

How can I check if the caller display feature has been re-activated as it was working previously before changeover ? 


Forum Team
Forum Team

Hey chops, thank you for reaching out and I am sorry to hear this. 

This will vary with your phone, if it working without this means your phone may not be compactable with this, you should be able to ask the manufacture about this.

Please do keep us updated. Cheers   

Matt - Forum Team

New around here?

Alessandro Volta

You'll need to borrow a modern phone with caller ID and check the service is still present on your line after the switchover to the hub (plugging the test phone direct into the VM hub via the VM adapter with no extension wiring connected)

If the caller ID service is present, are you connecting the caller ID unit direct to the VM hub or via your extension wiring arrangement (mentioned in your other topic)? For the purposes of testing the caller ID unit, connect direct to the VM hub ...

VM Hub>>VM adapter>>Caller ID display>>A single corded phone

The caller ID display unit seems to date from the late 90's based on online info. It may be expecting to receive a ringing signal via a 'bell wire' connection which is present in a telephone master socket but on in a standard VM adapter.

Thanks for the info, I have tried connecting it directly to the hub to eliminate anything to do with the extension wiring or REN number being exceeded. I suspect the caller display feature has not been reactivated after the changeover but haven't yet been able to contact VM on 150 due to excessive waiting times on hold.

With the old phone line system the ringing signal was an AC voltage sent down the line to activate the 'Bell'. Do you happen to know if this has changed or differs in the new hub system ? Maybe it is different and not compatible with older equipment ?


Hi Matt,

Could you check for me if the caller display feature has been re-activated on my account after the changeover was done,?




Alessandro Volta

You need to borrow a modern phone with a caller ID display (from a friend, family member, neighbour) and test your line to see if caller ID is still present. Trying to phone VM support is likely to only confuse the situation as they might tell you any random thing, which may not be correct/true if an appropriate solution does not appear on their on-screen script.

Once you have tested with a modern phone with a caller ID display you will know if it is present on the line. If it is not, you need to get it re-enabled and re-test your caller ID unit.

If caller ID is present on the line, and your unit is not detecting it, this could be due to the age of your caller ID unit.

Going back in time, the UK telephone network used a dedicated wire in the master socket for the ringing signal (referred to as the 'bell wire'). Over time, as more telephony equipment used in the UK started coming from overseas, the need for the bell wire has fallen out of use. Some older UK equipment, however, might still expect to use the bell wire. From topics on here the equipment that is affected seems to be from around the early 2000s and late 90s and before.

Some VM customers on here have reported a fix for the bell wire problem by buying an adapter with a ringing capacitor in it. This provides the third bell wire connection from within the adapter.

So test the line with a known good/modern phone which has caller ID on it first. The you can decide what to do next.

Sure, I will send you a PM now.

Please look out for the my message in your inbox. Cheers 

Matt - Forum Team

New around here?


Does that Called Id device work any better if it is connected (plugged into) to one of the telephone wall sockets as it would have been in the pre VOIP / Hub phone days ?

The reason I'm asking is the Master socket contains the ring capacitor that converts the 2 wire PSTN / HUB phone service to a 3 wire circuit.

In the 1st diagram, "From BT Network" has logically become "From Hub TEL 1" , the C1 capacitor brings the Ring Signal onto contact (3) of all the sockets.


I will have to experiment some more once I have confirmed that the caller ID display service is active on the service.

Is it possible to use a spare BT ADSL filter / adapter to restore the capacitor ? It was used to plug into a BT master socket and splits into a BT phone socket and RJ11 ? modem cable socket. I was told that this splitter also  incorporates a capacitor inside for the phone socket outlet.

You were correct about VM support on 150 as the call centre adviser said the Caller display feature is default activated always but seemed to be some confusion with what it is it and using the caller ID witheld option when you dial out....