MacOS – How to record a FaceTime call on OS X

This'll do it. You can input a phone number in most normal formats. Can't say I've tried them all:

set phone_num to text returned of (display dialog "Input a phone number to call:" default answer "")
do shell script "open facetime://" & quoted form of phone_num
tell application "System Events"
    repeat until (button "Call" of window 1 of application process "FaceTime" exists)
        delay 1
    end repeat
    click button "Call" of window 1 of application process "FaceTime"
end tell

I found it!

I tried many different combinations, such as facetimeaudio://[phonenumber] and facetime://audio/[phonenumber], but nothing worked. I was starting to think that there wasn't a way to do this.

However, today, I decided to take another crack at it with some different combos, and this one works: facetime-audio://[phonenumber].