Free directory assistance calls with 1-800-free411

Dial 1-800-Free411 to get free directory assistance. I just tried it and it works. How? Apparently they are using SR to narrow the search space as much as possible, and a human kicks in if they can't figure out what you said. I tried saying "Mercer Island, Washington" and it understood me, but after that it didn't seem to get me. It asked if I wanted business or residential, but sent me to a human when I said "business".