Pardon my ignorance, but the only free international Wifi calls I know of (other than Google Voice) that are as you describe are the ones embedded in social media. I can do voice or video calls on Facebook, FaceTime, WhatsApp, Zoom and probably some others.
The main requirement is both parties must use the same software. Other than Google Voice or Skype.
iPlum is a VoIP provider. They are not a carrier. They work over WiFi or Cellular. They provide a second line and phone number, mostly for businesses. Virtual PBX, multiple extensions, auto-attendant, etc.
But they are also like Skype, serving individuals with low prices for making and receiving calls on a real phone number. I could port in or out, so keeping my existing number was easy. They ported in my number from Google Voice in less than 24 hours. Anybody with a phone can call me if they know my number. From anywhere in the world.
Many of my calls are to U.S. businesses or government agencies. They all use phone numbers. Some are toll-free numbers, others just regular numbers assigned by their carrier. It doesn’t matter if their carrier is AT&T, Verizon, T-Mobile, Comcast, Orange, Claro, Tigo, or Skype, there is a phone number involved to reach me from any network, not just clicking on a profile in software. But it isn’t free, just very inexpensive.
So I can literally call anyone in the U.S. or around the world, with a phone number. No need to preplan a FaceTime chat. No need for them to have any special software.
If I am on FaceTime I cannot call my friend who is on WhatApp or Facebook. So, indeed it is free, but it isn’t very flexible.
But maybe I am just from a different generation that grew up on POTS and phone numbers. I live outside the U.S. and many businesses here use WhatsApp chat. I make doctors and dentists appointments on WhatsApp, order boutique food to be delivered on WhatsApp. It is very handy.
But if need to reach AppleCare in the U.S. it is an 800 number. As far as I know, they aren’t doing support over social media. But maybe I am misinformed? They do have chat off their website, but I prefer to actually talk to someone and screen share when appropriate.
Most of my friends are middle-aged or older. I’m 100 times more technical than they are. And the kids and younger generation is 1,000 times more technical than me. Older people like me are used to the workflow of telephone numbers. I call, or they call me, it rings, even if no app is launched. No need to pre-plan a meeting or call or teach them what app they need to download, so we can have a conversation.
Anybody in the U.S. calls my U.S. iPlum number never pays anything. If I call them from outside the U.S. using WiFi, or accept their call, it is $0.01 per minute. A penny a minute. That is from outside the U.S.
Inside the U.S. my carrier has unlimited local and LD calls, texts, and data. So, I just use the cellular network in the U.S. I even get international outbound calling to a group of countries for free as part of the plan.
So, if my understanding is faulty, and it could be, as it is hard to stay on top of technology, please reply and tell me. You CAN teach an old horse new tricks, at least this old horse.