If you're looking at Unified Messaging, Unity Connection is a very flexible platform. It can provide UM but it is not so tightly integrated with AD and Exchange that it ceases to function (or performance is degraded) when their are issues with backend systems. The Unity Connection implementation of UM is called dual store message synchronization. So, long story short - Unity Connection can operate as a system on it's own and be insulated from issues with other systems because messages are always stored locally and then it uses synchronization services to provide UM capabilities with Exchange. Messages are synched with Exchange and appear in the users INBOX but they are not exclusively stored in Exchange. With standard Unity (and Microsoft UM), VM is not just integrated with AD and Exchange but it is dependent upon those systems as message delivery and storage is dependent upon them. By decoupling these dependencies, the voicemail deployment with Unity Connection provides flexible options for the end user as well. With Unity Connection, you can specify whether users are voicemail only, integrated messaging, and/or unified messaging on a user-by-user basis. Why does that matter? Common scenario - legal departments aren't always so keen on the idea of having voice messages physically stored along with email and being subject to specific legal policies that may apply to email but not standalone voice messages. Another common scenario - some users love UM, some really don't. With Unity Connection, neither is a problem. Dissenters can be configured for voicemail only, use the telephone interface, have voice messages stored on Unity Connection and be happy campers. Those that love UM can be configured for Single Inbox, use the telephone interface, get voice messages in their INBOX, and be happy campers. Those on the fence could try Integrated Messaging and choose to a) go with voicemail only or b) graduate to Unified Messaging or c) stay with integrated messaging. You now have options that aren't so clear cut. The other nice thing about Unity Connection is that it is an appliance. No Windows patches, low maintenance, stable, and will obviously integrate with CUCM in either a SCCP or SIP integration without issue.
Is there something wrong with the other options? No, I don't want you to think that. Microsoft UM works just fine. AVST works just fine. There are other messaging options that work fine as well. However, there are things to consider for any solution. One common erroneous statement heard regarding Microsoft UM is that "it's free". It is not free. You need an Enterprise CAL to enable Microsoft UC options and an Enterprise CAL isn't free or cheap. If you already have an Enterprise CAL then maybe this becomes more attractive. AVST is very much like standard Unity. If there were such a thing as a blind taste test between applications, I can imagine that one could mistake one for the other in certain aspects. There are definitely differentiating factors between the two but they are undeniably similar at heart. You also have to think about who is going to be ultimately responsible for knowing the system, troubleshooting problems, and maintaining it. Common scenario - a voice system (such as Unity) is installed and it is tightly integrated and dependent upon AD and Exchange (or as Microsoft UM goes...it is one in the same); however, the voice team doesn't really grasp the integration with these other systems and likewise the infrastructure folks don't always understand that this new system is tightly integrated with their environment or they know it is but dont know just how much. This can make ownership and troubleshooting difficult. I've seen it (and still see it) regularly. If you work in a more collaborative and coordinated environment, this may be less of an issue and can open up the options a bit. However, if you work in a more disjointed or distributed environment then the ownership issue may be more of a factor. If the voice team is going to be ultimately responsible for the sytem then Unity Connection may look much more attractive since the architecture lends it towards both autonomous operation as well as integrated functionality. The learning curve may be less steep for the average telecommunications or voice engineer.
Before this becomes a novel, I'll address the question of pro's and con's for Microsoft UM vs. Unity Connection. Again, the best decision for each company isn't always easily drawn out in a clear cut list. You have to consider cost for any solution. Microsoft UM is not free. You need to consider the Enterprise CAL - you either buy one or you've already paid for it. If you have Unity and your support contracts are up-to-date then you may be able to migrate to Unity Connection in a very cost effective manner. You just have to do basic cost comparisons here to get an idea of upfront vs. recurring costs so you can compare. This is something you'd want to look at with your Cisco account team for sure. Then consider ownership and what would, on the surface, make sense for your environment (i.e., who is going to be responsible for the system). Of course, you also have to consider your requirements. If you don't care about UM (or just want to maybe use it) then going with a UM-centric solution could be cumbersome in the long run. Again, Unity Connection offers a lot of flexibility here. Last point would be to consider your existing infrastructure as well. With the 2003 implementation of Microsoft UM, you would still need a third-party product to be able to have MWI functionality. However, this is resolved with 2007/2010 and isn't really a factor at that point. Again, Unity Connection is flexible for UM here as well. You can integrate with a combination of Exchange 2003, 2007, and/or 2010 systems to provide UM to users and still have the basics covered from a functionality perspective.
I hope this helps...there is certainly a lot that could be covered on this topic and maybe too much for any single post.
Hailey
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