It would be nice if KDE Connect could actually accept and decline calls in addition to just muting them, and when accepting them having a persistent notification that allows hanging up and enabling speakers, potentially with an option to automatically turn on speakers when accepting a call. Reproducible: Always
I don't know if all of this is technically possible, but at least to the degree we can actually implement, it would be very nice.
Even though it might be confusing, because users might think that they can actually speak through their computer's mic and speakers. We will have to investigate if it's possible, and also how to present it to the user in a way that doesn't cause confusion. I like the idea of having the notification open while the call is in progress though.
I think answering and rejecting calls should be possible through "ITelephony". Thinking about it, however, it does not really make sense to be able to answer calls from your computer when you then cannot use your system's mic and speakers since your phone might by lying somewhere out of reach. But then it gets super complicated, although that would clearly be a killer feature ;) Indeed, having on-call controls where you can then end the call, activate speakers, hold, etc would be nice.
https://todo.kde.org/?controller=task&action=show&task_id=1561
If a bluetooth backend were enabled, I suppose the computer could use an audio sink and audio source profile, like a bluetooth head set profile. Then an answered call can be handled over bluetooth the using your computer's headphones and mic. Not sure if this is possible, just throwing it out there. (Note: I can already play music from my phone in plasma over bluetooth, so some part of it is possible)