Well, you tell me
I think it is good to reuse what is already developed, so I see using Android for phone functionality is the way to go. I could not make RIL for Android work yet.
My ideal result would be running Armbian on rock5b and Waydroid on top of it. But I need to build custom Waydroid image. So this is step by step plan
1 ) Make and Android image that runs on rock5b directly and makes phone calls
2 ) Apply the same changes to custom Waydroid image so that I can run rock5b as desktop (using armbian or rebornos) + as phone (using waydroid) at the same time.