System Settings (Settings (Station View))
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6.2.5. Ringtone Settings (Option Input)
Select the ringtone for an incoming contact input call.
Set a different ringtone for each source.
How to configure the ringtone
1) Identify the station to be registered in "Call source."
2) Choose a ringtone from "Ringtone."
Call Patterns 1 through 6, Tremolo sound, Busy tone, On-hold tone, Operation sound, Error 
sound, and Sound registered in "3.4. Custom Sound Registry" ➤ P.234
3) When done, click  .
4) Click .