@emphrath I have experienced once that a person i tried to call resulted in "phone number not known", even though the number was correct.

When receiving or making calls, the other person sometimes cannot hear me (even though I can hear them). Hanging up and re-calling sometimes fixes the problem, sometimes doesn't. I tried to figure out how to reproduce it, but it feels very random.
I figured that some telephone numbers work better than others. However, I haven't figured out which work better.
Has anyone experienced the same problem? How can I get more error output?