Help Call forwarding over internet

Hello everyone,

I'm looking for a certain set of features in an app (no problem if it requires root). I've googled it but didn't find anything that matched my exact requirements. Here are my requirements:

  • The app should have 2 modes: 1 mode receives calls on the simcard and starts an internet voice call, and the other mode receives this internet call and communicates with the original caller over internet and not wifi or bluetooth.
  • The oposite of this opperation can occur where the device that doesn't have the simcard issues a voice call to the device that has the simcard and makes a call through it.
The purpose of this is to be able to travel abroad and still make internet calls through a local sim card and appear local.

It would be great if someone can help me find an app with those features, paid or free, root or no root. I would also be of help if someone can help me by telling me the correct technical terms for those features so I can search better.

If no such app exists, can anyone help me by telling me if there are technical reasons that prevent such app from exisiting?

Thanks a lot!