[defenestrated]

Is there something like this but for calls?

Make your phone into an SIP/VoIP server? So that you can receive and make calls from any/many Internet clients while the Android phone with SIM is plugged in at home.

[Nexxxeh]

Like this software? Not that I've seen, but there devices that offer that functionality.

VoIP GSM gateways, sometimes with basic PBX functions, are absolutely a thing. Yealink do some (that I've not used) that act as a SIP registrar, you can basically log SIP clients straight into it.

And there are more heavy duty options that take 16+ SIM cards that are basically a rack-mountable mobile call centre.

[GranPC]

This would only be possible on rooted devices, and even then it could take some considerable effort depending on the manufacturer. The way call audio is routed on Android is SoC specific and often a pain to intercept or alter.

[liegon]

Maybe you could use something like Ubuntu Touch and utilize pipewire for the audio routing? Edit: I guess you should be able to use a script to route the call audio through to a Voip client running on Ubuntu and vice versa.