Fidelio supports user icons and custom button icons. However, the graphics need to be available to fidelio in the form of icon sets. These icon sets are available on the web and from the Window's client for Hotline. You can specify multiple icon sets, and they will be searched in the order given for icons and sounds. First match is used.
Note that icon sets also contain the sounds that fidelio plays when sound support is enabled, so you will need at least one icon set to hear any sound.
ExtractingIf you have access to Windows, you can download the Hotline Communications client for Windows, install it and find a file named "hotline.dat". Transfer this file to Linux and register it in the preferences, so that fidelio, when restarted, will use it.
Locally mirrored Icon SetsThere are some icon sets locally availabe for your convenience:
Please report errors and omissions to firstname.lastname@example.org