WiFi calling is a standard feature that does exactly what you describe for texts and calls, without using a third-party. I have cell connectivity turned off constantly on my phone and yet receive texts and calls via WiFi.
It is actually an awesome feature for receiving 2FA SMS at my parent's place where there is great internet but poor cell coverage.
Yes, indeed, how backwards. I wish I only used software that spied on me, or permitted others to spy on me, for those features.