Apologies if this is the wrong forum, but could find no other.
I have a BT 2200 deskphone which only works with the provided cable. My old cable does not work. I see the 'RJ11/?61?' plug on it has 4 connectors while the original only two.
Not a problem EXCEPT I have a line 'hiss' which is not present on my original deskphone using the 2 pin plug.
I can find no information on why the 4pins are necessary and wonder if there is something I need to do to my extension wiring to eliminate the hiss?