Over on Github, I just published some code I wrote to implement support for “tel:” links for Google Fi’s Messages for Web app on Linux.
In other words, if you have Google Fi and you use Google’s Messages for Web app on Linux, then once you’ve deployed my solution, if you click on a phone-number link in your browser and select “xdg-open” to open it when prompted, or if any other application that uses GNOME file-typing system tries to open a phone-number link, the phone number will dial in Messages for Web automatically.
I spend most of my day nowadays on a Mac instead of on my Linux box — since we are all Mac at work — so I’ll eventually implement this for macOS as well, assuming someone else doesn’t do it and submit a PR before I get to it.
UPDATE: I did a lot of work on the macOS application and got most of the way there, but there’s a blocker I can’t figure out how to solve. Please email me if you’re a macOS developer and you’re interested in pitching in and I’ll fill you in on the details.