When it comes to Voice Messaging there are two models which can be used. Since there are similarities between integrated and unified messaging, there is often confusion around what the two terms actually mean. Many vendors are actually even using the two terms to mean that same thing even though they are quite a bit different. Lets break the two down a little bit and try to clear up some confusion.
Unified Messaging - Unified Messaging as a term has been around for a while, and was even awarded the #1 spot on Wired Magazine's hype list of 1998, but many are unaware of what it really means. With Unified Messaging you are using an existing mailbox store i.e.. Microsoft Exchange or Lotus Domino. So the voicemail system answers the call, takes a message, and then packages that message up into email format and sends it over to the email system. So what does this get you? Unified messaging is advantageous in some instances since you only have one mailstore to manage, which means all of your email and Voicemail is stored in the same place. So when you are looking at Disaster Recovery, redundancy, or storage you look at the voicemail and email together. The other nice thing about Unified Messaging is in setting up the user clients. When all of your messages are in one mailstore you don't have to worry about setting up 2 clients, or having multiple accounts set up on the same client. You also see all your messages together, which depending on how you work can actually be a benefit or a real pain.
Integrated Messaging - Now that we have an idea of what Unified Messaging is, lets take a look at Integrated Messaging. Where Unified Messaging is built on the idea of a single mailstore, Integrated Messaging products like Unity Connection use a separate mailstore or message store to hold the voice messages. If you have an existing email system deployed you don't have to touch it to get up and running with Integrated Messaging. The email system will still be used to handle your email, but instead of having the voicemail system drop messages on your email server, it will store them in it's own mailstore. From a users perspective there would be an additional mailbox in their email client, and depending on the mail client this would either show the voicemail with the email appearing as a single mailbox or would require the user to select the voicemail folder in the client. This could cause a little more work on the administrative side up front but is easy enough for users to do with a little guidance.
Like Unified messaging Integrated messaging also has its advantages. One of the biggest advantages I see in Integrated Messaging is that it is not Unified Messaging. What I mean by this is that the messages are not grouped in with your email messages, for most of us our email boxes see a pretty high volume of input, cramming voicemail into that same email box will only hide the important voicemail. I will still see my MWI if I am sitting at my desk but then that really defeats the purpose of having the voicemail in my inbox. With Integrated messaging I have a separate mailbox just for my voicemail, and I can tell right away by looking at that mailbox that I have a new voicemail. Another advantage to Integrated Messaging is not being dependent on your email system. Email systems have many moving parts and when you base your voicemail on an email system you are really at the mercy of the email system. Updates and changes on the email side have to be tested and verified to work with the voicemail system, and the email and voice guys need to talk to each other, though we do recommend this practice of talking to each other regardless of whether you go unified or integrated, it really does make things easier.
The other big issue between Unified and Integrated has to do with electronic data retention. I will not go into too much detail on this one since I am not a lawyer and your restrictions may vary depending on your industry. The short of it is that because integrated messaging does not store voicemail on your email system it may be subject to different retention policies. This area is constantly evolving so it is important to talk to your legal representatives about how this will affect your voicemail deployments.
I hope that this clears up some of the confusion between Unified Messaging and Integrated Messaging. There are many other advantages and disadvantages to both methods but I really just wanted to lay out the framework of Unified and Integrated messaging and make it as straightforward as possible. Feel free to post a comment if this brings up any other questions or if you need any clarification on the topic.
Technical Marketing Engineer
Unified Communications BU