Why does the US share country code?

Answer 1

The United States shares its telephone country code +1 with Canada and 18 island countries and territories in or near the Caribbean.

There is a lot of telephone traffic across the US/Canadian border, and the telephone systems are integrated so that a call goes as directly as possible from one regional switching center to another, to its destination. For example, a call from Seattle to Vancouver doesn't have to go through New York and Toronto on its way. The systems were closely linked long before the system of international country codes was devised. It was thus much easier for the two countries to continue to share an integrated dialing plan.

Calls to the various British islands in or near the Caribbean were historically routed through the United States, so it was easier to integrate them into the US/Canadian system, now known as the North American Numbering Plan.

The Dutch island of Sint Maarten in the Caribbean joined the North American Numbering Plan in 2011 for economic reasons. It's easier to persuade a U.S. or Canadian resident to call 1-721 as opposed to 011-599, even though it makes no difference in the cost of the call.