The number nine...?

Question

Why do we dial the number nine first when making outgoing

phone calls from some buildings?

Answer 1

This is because most large office buildings will have a switchboard system that allows you to dial between rooms within the building by typing a short extension number.

In order to dial to a number outside of the building, most systems require you to press 9 first, so it does not try to contact someone's extension inside the building instead!

Answer 2

The PABX or the switch board at the building has a CO lines and extention lines.

The ext lines normally 3 or 4 digit numbers only that can be dialled directly. To enable an ext line to call outside line(outside the building) it should dial a 9 to access the CO line. Why 9? It is the highest digit at it mostl likely will not be used as the beginning of an ext number.

Answer 3

Just a standardised way of PBX, some use 0 (zero)