I couldn’t make calls to landlines (iPhone 15 pro). I followed all the steps suggested on here like resetting network settings, toggling airplane mode on/off etc but nothing worked. ChatGPT told me that I needed 4G Calling (VoLTE) enabled. I did not have the setting on my phone to do that. It was something iD had to do. Their chat support was suprisingly good and enabled it in a few minutes but I went to them with the solution. I wonder why it is not enabled as standard. Seems like it should be.