I do not know about the Mini, but I think you could create an intercom key set up for voice.
We have several of these, set up like this:
xx DIG yyy zz V/R
The yyy is the intercom group, and the zz is the member number. The V/R allows you to be connected using a ring or just an open line where you annouce your presence.
The way this works is to set up on multiple phones, each with the same group memeber (0-2045) and a unique member number (this does not have to correspond to your dialing plan, and can be anywhere from 0 - 99). Then select the DIG key and dial the member number you wish to call. In this case, you would not need to answer the phone to have an intercom conversation. If the phone has HFA set in the class of service, it will be connected in a hands free state. We used the last two numbers of their DN to make it easy to remember.
A WORD OF WARNING HERE!!!!!!!!!
I had a situation where a Prsident used this to listen in on other employees conversations. He would dial there member number, then hit mute on his own phone. As I remember, there is not a buzz when the call is connected, so he would start the intercom connection when they were talking and never announce himself.
Hope this helps. I am not sure if this will work on a Mini, but I am fairly certain a 3900 phone will accept the key without any problems.
Scott M.