Why some countries use trunk prefixes like 0 or 1?

Some countries use trunk prefixes (like 0 or 1) before dialing a long-distance number within the same country. This prefix signals the telephone exchange system that the call is not local but a domestic long-distance call.

For example:

• In India, the trunk prefix is 0. So, to call Mumbai (022) from another city, you dial 0 + 22 + number.
• In the United Kingdom, it’s also 0.
• In the USA and Canada, 1 is used as the trunk prefix.

These prefixes were introduced for technical reasons in traditional landline systems to differentiate between local and trunk (long-distance) calls.

Even though most mobile phones now handle this automatically, the prefix system still exists for consistency and ease of dialing. In short, a trunk prefix tells the telecom system: “This call is going to another area or state within the same country.”