This really isn't that unheard of...it really just depends on the specific requirements and circumstances of the customer when one or the other was implemented. As for the use of Unity for UM, traditionally Unity has been the only product Cisco offered that could provide true UM. However, this has now changed with the release of Unity Connection 8.5(1) but this is very recent. For existing customers there was no other Cisco product offering so if you have an existing install base and they wanted UM capabilities with a Cisco product, then they would had to have installed Unity.
The addition of Unity Connection could be based on a number of things. It may be that the customer was intrigued by the Linux platform and looking to possibly move away from the Windows-based Unity product and associated maintenance, etc. In some cases I have also seen that companies install UM only to find that some departments (typically legal) have issue with this. So, they will install a voicemail-only system that is separate of Unity to ease those concerns. Really, there are many reasons why your customer may have both products so these are just examples and without details are speculation but I've seen it before.
As for integration between the two...it depends on what you want to do and I believe there may be some version requirements as well. But there is digital networking that may be useful depending on requirements. If you mean integration with the same CUCM, this isn't a problem. You can integrate multiple voicemail systems with CUCM simultaneously without issue. You just have to ensure you manage settings for end users properly (i.e., users are forwarded to the correct system via the VM profile assigned to the phone).
Hope this helps...if you have more questions, just post them back.
Hailey
Please rate helpful posts!
