Could you implement the Call Manager 6.x or last with Unity Connection. Implement a Call Manager Publisher and other such as Subscriber. I belive that you can be use the gateway Cisco 2821 with 1 FXS - Four ports.
You have knowledge with Call Manager implemention?
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...