1. Simple - send a link which which friend opens on their smartphone
2. You chat
3. FREE + opensource
4. Audio quality is better than PSTN, skype, Zoom etc
5. All done in the browser no app to download or install for your guest - or you

You'll need

1. a smartphone each
2. decent internet
3. a way of communicating the desire to talk, SMS, email, etc

2. https://pipe.github.io/two/ this creates a link,
3. share the link with your friend But you can use twitter DM , SMS, email, whatever works for you both
4. Click 'Done' - allow Microphone use and wait for your friend to join.
5. Your friend opens the link, accepts the call and enables the microphone use. (you must click 'Done' before the friend 'Accepts')
6. Talk. place the phone somewhere comfortable, adjust the speaker volume and just talk. (The mic symbol mutes/unmutes your microphone, the square ends the call). You can use earbuds/headset/airpods if you like.
7. At the end of the call click the square button

Enjoy!

The UX needs a re-work so it fits on multiple screens