I was job hunting and my mom was watching TV and heard 555 be the start of a number. When did this start?
In 1973. Before that, filmmakers would usually get fake/unused numbers from the phone company—but unused in what area code? As long-distance calling became more commonplace, prank calls to the numbers given became more of a problem. People in virtually every area code still call 867-5309 and ask for Jenny.
Oh, and here's the phone directory. Nowadays, only 555-0100 through 555-0199 are reserved for fictional use, and the other numbers have been released for actual assignment.