6-1-1 is a special telephone number in the United States and Canada. It is the number to call for phone service customers when there is a problem with phones in an area, or when a payphone is not working properly. Many mobile phone service providers use 6-1-1 as a customer service number.
The Federal Communications Commission did not officially decide that the 6-1-1 number should be used for this. They decided to let it stay because it had already been accepted, or chosen, by the North America Numbering Plan.