we just switched to D345 Telephone.
With our old Siemens OPTIPOINT we used
Zweithörer SIEMENS ZFH 71 für Telefon
Do you have a Idea how to use it with the SNOMs?
You may want to contact Siemens and see if they provide an adapter for this device that allows it to connect to the 4P4C headset connector on our phone. You could then test its compatibility.