A telephone number or phone number is a sequence of numbers used to call from one telephone line to another in a public switched telephone network. When telephone numbers were invented, they were short — as few as one, two or three digits — and were used by people to call a few neighbors. As phone systems have grown and interconnected to encompass the world, telephone numbers have become longer. In addition to telephones, they now access other devices, such as computers and fax machines.

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