Ok. In the meantime, I did a clean install. Nevertheless, phoning does not work. I can’t hear other person, other person can’t hear me. Clicking “hold the line” let play an according automated annoucement at the other person’s phone (presumably generated by the provider). Clicking “hold the line” at the other person’s mobile gives no change in the silence I’m hearing.
In order to circumvent problems of the included SMS app one can install the same (but unforked) SMS app (ref. there). Analogously, I found the app “Telefon” by Google, but installing it doesn’t seem to work. (After downloading with the Apps-app, there appears “Installing” – but did not disappear for about half an hour).
Is installing another phone app a suitable way?
Are there any suggestions?