[Hampshire] Domestic Telephone exchange

I have an office at the end of the garden and my wife has one in the
house. For many years we have had a Panasonic KXT 206E Telephone
exchange which has enabled us to transfer calls to each other (and even
play "Greensleeves" to the caller while waiting). It also has a door
intercom which is handy when there is nobody in the house.

It appears to be coming to the end of its life and I would like to
replace it with something similar. This sort of functionality seems to
be provided by wireless DECT phones but my wife is a bit reluctant to
introduce more wireless into the house. Does anybody have any
suggestions for something to use the existing cabling.

Thanks

Roger