Thanks for the fast reply.
I just tried out all of the constellations, but of no luck. When used with a trailing plus the addon refuses to start at all based on the following error: “pjsua_app_config.c Error: invalid SIP URL ‘sip:+49301234567’ in local id argument”
All the other number variants were used by the addon and with a test call through the dev tools according to the protocol of the addon it was in the state of “CALLING”, but on fritzbox-side there were no sip-registrations active, or any call attempts visible.