Intercom and Barge-IN:
An intercom line is a dedicated two-way audio path between two phones. Cisco Unified CME supports intercom functionality for one-way and press-to-answer voice connections using a dedicated pair of intercom directory numbers on two phones that speed-dial each other.
If we have to c0nfigure Intercom between two phones..lets say between a manager phone and his Secretary..so that both these intercom numbers are not reachable from rest of the cluster and are not dial-able. This is how we can configure this:
ephone-dn 9
description Manager
number D40 no-reg primary
intercom E50
!
ephone-dn 10
description Secretary
number E50 no-reg primary
intercom D40
!
ephone 1
button 4:9
!
ephone 2
button 4:10
In the above configuration, both users can Intercom each other when they are not busy on another line. Lets say Manager wants to Interrupt even if Secretary is on the phone. To do that we will have to configure ‘barge-in‘ at Secretary ephone-dn.
ephone-dn 9
number D40 no-reg primary
intercom E50
!
ephone-dn 10
number E50 no-reg primary
intercom D40 barge-in
ephone 1
button 4:9
!
ephone 2
button 4:10
Whisper Intercom:
When a phone user dials a whisper intercom line, the called phone automatically answers using speakerphone mode, providing a one-way voice path from the caller to the called party, regardless of whether the called party is busy or idle.
Unlike the standard intercom feature, this feature allows an intercom call to a busy extension. The calling party can only be heard by the recipient. The original caller won’t hear anything coming from called-party.
ephone-dn 24
number 3001
whisper-intercom label “Marketing”
!
ephone 24
mac-address 02EA.E789.B765
button 1:24
Here if someone dials 3001, they can say whatever they want as the user at ext 3001 will hear them but they can’t hear him.
voiceonbits.com 
PH- A- 3001 PH-B – 3002 PH-C – 3003
Option- I:
PH-A
ephone-dn 16
intercom A3002 no-mute
Dialed 3001 from 3003 , answer from 3001 , showing connected on both 3001 and 3003.
INTERCOM from 3002 —— PHONE WAS JUST RINGING.
Option -II :
ephone-dn 16
intercom A3002 no-auto-answer
Dialed 3001 from 3003 , answer from 3001 , showing connected on both 3001 and 3003.
INTERCOM from 3002 —— PHONE WAS JUST RINGING.
Both cases I found the same result.
My question here is what is the difference between no-mute and no-auto-answer ?
Thanks
Cisco CME’s intercom function is built using two functions:
# Autodial at the initiating end of the intercom
# Autoanswer-with-mute at the receiving end
The syntax is:
intercom extension-number [[barge-in [no-mute] | no-auto-answer | no-mute] [label label]] | label label]
no-mute is used to take off the default mute feature from intercom. To respond to the intercom call and open a two-way voice path, this is used. The benefit is that people who receive intercom calls can be heard without them having to disable the mute function.
The auto answer feature, the called phone automatically answers the call in speakerphone mode with mute activated, which provides a one-way voice path from the initiator to the recipient. A beep is sounded when the call is auto-answered to alert the recipient to the incoming call. No auto answer will make the phone ring till the other party picks up the phone.
Hope this helps.
Good post, although dated i picked up some tips, do you have anything relating to CUCM version 9.1+ ? Thanks