The Imagination is an old TDM/ISDN key system. We still maintain a few but they are on thier last legs to be honest. The main board comes with 9 digital ports to which you can connect either 2 keyphones (isdn terminals) or 1 x BRI trunks. There was also expansion cards to add analogue or isdn ports.
In my opinion if its working then run it until it causes more problems than its worth (if that goes to form I'll give it about 2 weeks!
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I may have programming maps etc somewhere. I'll have a look and post back.