If you do not wish to have any acoustic signal when a call is received, select the option “no sound” from the drop-down list "Ringing" for this number, see To define different ringing sounds step (6). SwyxIt! Classic will then signal an incoming call via the interface, e.g. an animation of the line or – if it has been configured in the user profile – by a SwyxIt! Classic window in the foreground or an information balloon.