A Public access branch exchange is a smaller
phone exchange that is used by one company or in one building.
The PABX is owned or rented by the company. The reason
for using a PABX is that in a company that has more than a few
employees it would be expensive to get single phonelines
to every phone. The PABX makes it possible to call from one
phone, connected to it, to another without using the public phone system,
thus saving money on the phonebill.
Also internal numbers are shorter. Modern PABX'es offer many
spesial services like the possibility to connect wireless
phones and automatically transfer calls. Some can even be interconnected
over leased lines and act as one. This means a company that
is spread over a large geographical area can use short
numbers.