@llelectronics: Thank you for the update and providing the APK due to "frozen" Jolla store.

I still want to learn more about, how Signal works, but tried your port already out. How do calls work? Whenever I click the call icon, the Jolla UI asks me to start a regular call over chosen number. Unfortunately I don't have any contacts yet (!) using signal.

Does Signal on Jolla start calls over data connection whenever the other user has Signal installed as well? How does it work on Jolla?

Thanks for your help and sorry if I ask stupid questions ;-)