To answer this question, you need to take a good look at your internal telephony system that you already have in place. Basically, the ones that are supported by Microsoft Exchange Server 2007 Unified Messaging (UM) are: Key telephony, Centrex and PBX. Find out which kind you already have. Chances are that you already have a PBX system in place.
Once you’ve identified the telephony system that you are using, its fairly easy to determine if you need a VOIP Gateway. There are two kinds of telephony networks: Circuit switched network and Packet switched network. IP falls under the latter. Normally the line from the telephone company uses circuit switching. Exchange Server connects to IP network, so it needs packet switching. A VOIP Gateway just does that: it converts a circuit switched network to a packet switched one.
Whether or not you need a VOIP Gateway can be summarized as follows.
You DON’T NEED a VOIP Gateway if:
You are using a PBX telephony system, and you have an IP-based PBX
You are using a Centrex telephony system and you have an IP Centrex.
You NEED a VOIP Gateway if:
- You are using any kind of Key Telephone Exchange
- You are using a PBX telephony system, but you don’t have IP-based PBX
- You are using Centrex telephony system, but not IP Centrex.
In short, if your telephony system doesnt support IP, you need a VOIP gateway to convert to a packet switched IP network.
There is an e-learning product on the Microsoft Learning web site which is available for free for a limited period. Check it out: Clinic 5091: Introduction to Microsoft Exchange Server 2007 Unified Messaging.
See also: Preparing for Unified Messaging, Part 2