Why do people exchange numbers?

Communication through phone is a more intimative way of socialising with people. This is the main reason why people exchange their phone numbers to know more about the fellow people in many ways. To have an option of calling them if they want to.

What are the parts of a telephone number?

Area code and other parts of a phone number Phone numbers in the United States typically consist of 11 digits — the 1-digit country code, a 3-digit area code and a 7-digit telephone number. The 7-digit telephone number is further comprised of a 3-digit central office or exchange code and a 4-digit subscriber number.