If you do not have an NTE5 master socket with a removable lower half or if your extensions are all connected using plug-in adapters or splitters, it is possible to disconnect the bell wire by the following method which has worked OK for me.
Cut a thin strip of electrical insulating tape 3mm wide and 40mm long and stick it lengthways along the plug that goes into your master socket. Place the tape so that it covers the two middle pins (3 and 4), but leaves the two adjacent pins (2 and 5) exposed. Wrap the tape back along the other side of the plug so that it is stays in place when inserted.
See my photo at
This will disconnect the bell wire, without the need to cut or remove any wires.
Check that the phones still ring OK. If a problem does arise the tape can be easily removed,