Are there technical limitations that prevent forwarding calls between devices over wifi?

I'm wondering if there are any restrictions placed on apps that would prevent audio forwarding for calls. This is what I imagine: - You have two Android phones, phone A and phone B - Phone A has a sim card and is left in your host country connected to WiFi - Phone B does not have a sim card, and is with you when you travel to another country, but will have WiFi - When phone A receives a phone call, phone B will ring and you would be able to answer the call. Keep in mind this would happen over WiFi - You would also be able to make calls from phone B, and it would be routed via WiFi to phone A What I've noticed when looking for apps is: - text forwarding and receiving is plentiful, tons of apps do this but not for calls - VNC apps such as TeamViewer or AnyDesk do not forward audio from phone B to phone A - There is a hardware solution for this, but it's subscription based ( https://www.glocalme.com/product/simbox/ ) There's been some interest in this topic, but no answers: - https://xdaforums.com/t/call-forwarding-to-no-sim-phone-help-pls.3448976/ - https://android.stackexchange.com/questions/202099/controlling-phone-and-making-calls-remotely This leads me to believe that this is not possible, but why?