Hi:
Good instructions from Obihai, except for one typo: the step "3b" (the line between 3 and 4) should read:
"Make a call through Gmail using Google Chat, to any phone number, and then hang up."
Hangouts is the new system that replaced Chat, but you can leave the old Chat destination in place solely to support your OBi for now, and you can then switch back to Hangouts (click "Try the new Hangouts").