411

411 is the telephone number for local directory assistance in the United States and Canada. One exception is the Pacific Northwest, which used 113 until the mid-1980s. Until the early 1980s, 411 local calls were free in most states.
411 has also been used for long-distance directory assistance in most areas in the United States and all of Canada. The traditional long-distance directory assistance number is 1-area code-555-1212.
411 is also commonly referred to as "D.A.", "Directory Assistance", or "Information".
Approximately 6 billion calls are made to 411 within the United States every year.

Source: http://en.wikipedia.org/wiki/4-1-1