What is the SMS/800?

The SMS/800 Data Center houses the main database of available toll free 800, 888, 877 and 866 phone numbers for the United States and Canada. The SMS/800 maintains and updates the database and keeps records of the owners of each number. Available numbers on the database are assigned to subscribers on a first-come, first-served, basis. SMS/800 keeps records on the status of all 800 numbers.

Read more here.