The Contacts+ Exchanging an Authorization Code Java Sample Code demonstrates how to access the Contacts API that contains a client ID and a client secret. The API response body shows the client's OAuth code.
FullContact's CEO, Bart Lorang, has just posted the company's 5 Laws of Privacy. Small wonder--they are in the business of upgrading your contacts by providing an address book in the cloud that fills in contact details. Any user would have a simple question: what happens to data I give to the company?