technical - security with a landline from hackers

[#1]

I am trying to help the widow of an extremely wealthy man whose home is adjacent to the famaily business, which has now been taken over by the daughter from a previous marriage.  Relations are rock bottom and my friend has been left penniless in the will.  Sadly, she is now involved in legal action as of course she is entitled by law to reasonable financial provision.  The step-daughter is quite shameless, evil and greedy.
The landline to the house goes past the business premises, and there used to be an extension from the house to the offices, which meant that all my friend's calls to her solicitor could be overheard in the office, until she got someone to come and pull the wires out from the telephone socket.  That seemed to work until recently, when she has noticed on her Caller ID that she now suddenly gets a message which reads "Extension silence".  That was not there before, even after the wires were disconnected which was some weeks ago.  It has only just started to happen, which makes her very suspicious that her landline may have been tapped into and a new extension installed in the office.
This situation is bordering on fiction, and the step-daughter has been up to many dirty tricks, including fitting a GPS tracking device to my friend's car wiithout her knowledge - it was not very subtle and was disovered by her garage when the car went in for maintenance !  The telephone bill is of course paid for by the business, and installing a new system with new wiring would be impossible because access to her house is via the business premises.
To make matters worse, the mobile phone reception is also impossible, because there is no signal indoors from any of the mobile phone companies.  At present, she is having to rely on going out to make calls to her solicitor where she can find a signal, which is not very practical, and to rely on email communication.  This is not an exaggeration; as I said, it sounds like something from a novel.
My question therefore is whether anyone knows what "Extension silence" might signify, and why it has suddenly started to appear when it was not there before.  Secondly, of course, whether anyone knows whether there might be some sort of encryption device which could be fitted to her landline to ensure security.  I have  thought about VOIP which presumably would be secure, but she is an elderly woman who could never get her head around using a computer to make calls - it is all she can do to read emails, but she does not know how to reply to them !!  Any practical suggestions would therefore be appreciated.

[#2]

If she has a new style master socket, one thing you could do is use the test socket. First however I'd unplug the phone and then try ringing the number. If they've wired in an extension before the master socket it will ring (and if they are stupid it will be answered).  If you happened to be outside near the office you might be able to hear it ringing. If you can prove they have done that you could then report them to BT for interfering with the BT wiring.
If she has broadband, using VoIP with either an enabled router or one of the devices that plugs in to the router would mean that using the VoIP phone would be very little different to using a normal phone.

[#3]

Hi jelv
Thanks for the answer.  I will try the test socket.  But I would have thought that as a caller, I would still get the ringing tone even if it was not actually ringing, wouldn't I ?  Whatever happens, I can certainly get her to go near the office to see if it rings there.  That is an excellent idea.
What I have discovered is that the broadband service is not fed from the same telephone number as her landline, because when I telephoned BT to try to talk to someone about it, their automated service asked me to enter her number, which I did, and it then reported that there was no broadband registered to that number.
Therefore, the broadband must be an extension from the office broadband modem.  I imagine that they must have connected a WiFi router in her house to the office modem, which would explain why her landline number has no associated broadband.  That makes matters even worse because she may also be networked to the office computers, in which case they could even access her laptop !  I imagine that if I check her computer, I should be able to see whether  her folders are "shared" or not.
I have just spoken to her and she tells me that she has just heard someone lift a receiver somewhere .... So I think there is little doubt about it.
One other question.  If she were to use Skype on the broadband, I imagine that she could not be overheard even on the same network because it is encrypted surely ? It should be secure as far as I understood.  Is that so ?  I understand that a VOIP phone would not be, but Skype needs a password.

[#4]

[quote=shermans]To make matters worse, the mobile phone reception is also impossible, because there is no signal indoors from any of the mobile phone companies.  At present, she is having to rely on going out to make calls to her solicitor where she can find a signal, which is not very practical, and to rely on email communication.
Has she considered using a femtocell ?  -  http://en.wikipedia.org/wiki/Femtocell
I believe you can get them for most mobile operators,
for example here is the Vodafone solution - http://www.vodafone.co.uk/personal/price-plans/network-and-coverage/sure-signal/index.htm

[#5]

purleigh
Fascinating.  I had no idea at all !  Thanks for that; I will look into it.

[#6]

A thought: if I were the daughter in law and I found m-i-l was using broadband to make calls they couldn't intercept I'd kill the broadband.

[#7]

A risk that I had not thought of.  However, it would not look good for the step-daughter when this goes to Court as it would demonstrate just how vindictive she is.  My friend's Barrister is advising that she has a watertight case under the Inheritance Act, and is acting for her on a no win no fee basis, which demonstrates his confidence because they were married for more than twenty years - she should be awarded as much as would have been the case if they had been separated as the result of a divorce rather than by death, so she should get 50% of the estate.  But it will take two years to come to Court.
If the step-daughter did kill the broadband, I imagine that an interim injunction would have to be sought, but I would hope that it will not come to that.
Thanks for the warning though.

[#8]

I would suggest that the daughter-in-law is very unlikely to make the connection that the mobile phone calls were being routed over the internet, as most people have no idea that it is even possible.  She would just see a mobile phone being used, and would have no reason to associate the usage with an anonymous looking network box - especially if it was hidden out of sight and connected using mains networking homeplugs.