If this works without proprietary software, it might actually convince me to use Signal.
I already have a VoIP phone number through JMP and would be happy to use it for Signal, but I've read that registration isn't an option on the desktop client, even if I also have a phone number. I looked for a fork or alternate compatible client that allows registration but didn't find one.
It's an absolute pain, but you can use signal-cli to do it (or at least you could a few months ago when I did). Just an FYI if you ever have time to burn.