Centrex:

A PBX is similar to a localised phone system, with each line having only a three or four-digit phone number. Companies prefer PBX because it saves money, while employees love it because it makes numbers easier to recall. An IP Centrex phone system is a telephone company-provided service that simulates a Centrex PBX system.

A telephone service in which the telephone company's facilities house an IP-based PBX. Rather than using telephone lines, it connects to the customer over a local area network (LAN).IP CENTREX provides voice-over IP and other IP-based services and standard telephone system connectivity (PSTN).

Zones are not limited to Centrex IP. It's a service that covers the entire country of India. A customer can have a PAN India IP centrex service, which means that numbers across India can be combined into a single Centrex group. Each group member can communicate with the others by dialling a shortcode.

You can activate the Centrex phone system on your Airtel landline by dialling 121 and asking for CENTREX to be activated. They will request three numbers from those who are already members of the Centrex Group. Once activated, dial # and the last four digits of the Airtel landline number to reach all group members.

Incoming calls can be dialled directly without the intervention of an operator using the Centrex technology. Every telephone served by the Centrex system is directly connected to the telephone company switching centre, and the Centrex equipment is situated at the local telephone company's central office premises.

Centrex and VoIP have one thing in common: they're both hosted services with a set contract pricing. Both of them carry voice traffic. The similarities, however, end there. Voice over Internet Protocol, or Centrex VoIP, is a voice that flows over the internet, as the name implies.