The official Snom ring tone is terrible. It sounds ominous. 3CX has decided to leave this ominous ring tone the default for all internal calls. If you’d like to change it, you can.
I’ve been testing with other Snom phone in my office. It seems 3CX has changed the way they do distinctive ring. 3CX used “Alert-Info” headers in previous version of the phone system. As of version 14, they don’t (They may still do it for a distinctive ringer on queue calls)
For internal calls, they now use a directory entry. It seems that any internal looking extension, the Snom phone considers to be a “Colleague”
If you go to the Snom phone web ui, and click on “Preferences” in the left menu. Scroll down until you find the “Directory Ringtones” section. See attached image