WebCall can be used as the main phone app, for instance on Wifi-only devices.
It works without a SIM & lets you receive calls from anyone on the Web.
Based on WebRTC, it can make & receive high quality audio/video calls, all calls connect via a direct link between 2 devices, no media server or router involved. All calls are always e2e-encrypted. Calls start as audio-only, you can add video at any time during the call,, comes free of trackers, analytics, telemetry, etc.

timur.mobi/webcall/android/