There is no one-size-fits-all architecture. Microservices are fine, but probably not for you.

KDE Connect? Edit: It doesn’t look like that supports calling. But it does texting

The location permission is because in dense cities there are enough unique, stationary bluetooth endpoint that you can guesstimate a location.

External communities are just searchable, subscribable and browsable from here. Sometimes you need to change a search filter or default view from Local to All. Or is there something else you feel is missing? I think 90% of the issues people are having are UX related and not a core issue with federation or decentralization.