FritzNotify is a desktop-application to handle call-signaling from callmon (running on an AVM-FritzBox!). It supports output in english and german. By default german will be used as the FritzBox! is mainly used in germany.
It uses notify-send to inform about incoming calls, outgoing calls and terminated calls.
It asks www.tellows.de for the ranking of the calling number.
For incoming calls, espeak and mbrola are used to read the number and the score reported by tellows.de out loud.
While a call is active, the speakers get muted.
Therefore: If you listen to music from your computer but are not in front of it at all times, you
dont't need to mute the music before picking up the phone.

FritzNotify expects up to two alsa-configured soundcards (like i have). If you have even more
soundcards, i guess you know what you are doing and are aware of what needs to be done to mute
those other soundcards as well. ;-) (e.g. tweak fritznotify-mute-all and fritznotify-unmute-all)

espeak (and mpg321, which outputs the mbrola-speech-output) outputs on the default soundcard (pulsaudio on recent systems).

Now by default mbrola is used for speech-output. The voices for mbrola get downloaded on demand and are not part of fritznotify-packages.