Snom 300 with headset: Unlink ringtone volume from headset volume

If your Snom 300 always keeps the same volume for headset and ringtone (as soon as you change one you also change the other), here's what to do:

Go to your phone settings web interface, then Preferences (German Präferenzen). There is the seemingly harmless setting for Ringer Device from Headset (German Klingeltonausgabe bei Kopfhörer). Choose one: "Headset" or "Speaker". Do not select both, otherwise the ringtone volume will always be the same as the headset speaker volume!