I used to have a detached shop with an extension of our house phone. Since my wife couldn't call our own phone, she would call her mother, have my MIL call the house, and let the phone ring until I picked up. If you think getting interrupted in the shop is bad, try getting interrupted by your mother-in-law EVERY TIME!
Man, I used to LOVE to just let that phone ring and ring. Of course, there is always a price to be paid...