Hi Roberto,
Intercom is really an "always on" feature as described below. The Intercom call is answered in a Whisper state unless configured to;
Auto Answer (on an Idle Line state)
- With Headset
- With Speakerphone
Intercom
Intercom, a new type of phone line, combines the functionality of a traditional line and a speed dial. With an intercom line, a user can call the intercom line of another user, which auto-answers to one-way audio whisper. The recipient can then acknowledge the whispered call and initiate a two-way intercom call.
Users can use an intercom line to dial any other intercom line in the intercom partition, or the administrator can preconfigure the line to target an intercom line outside the intercom partition.
Note 
Users can use an intercom line only to dial other intercom lines.
Introducing Intercom
Intercom allows a user to place a call to a predefined target. The called destination auto-answers the call in speakerphone mode with mute activated. This sets up a one-way voice path between the initiator and the destination, so the initiator can deliver a short message, regardless of whether the called party is busy or idle.
To ensure that the voice of the called party does not get sent back to the caller when the intercom call is automatically answered, Cisco Unified Communications Manager implements whisper intercom. Whisper intercom means that only one-way audio exists from the caller to the called party. The called party must manually press a key to talk to the caller.
Note An auto-answer tone will mark the beginning of the whisper state for both the sender and the recipient.
http://cisco.biz/en/US/docs/voice_ip_comm/cucmbe/admin/6_1_1/ccmfeat/fsintrcm.html#wp1047595
If you want a setup where the Manager has to press a Line button before the Intercom-style call is connected, here's
what to do;
On the manager phone create a new Line/button with a new DN...let's say it's 2511 with a Line Text Label called Intercom.
This number is a non-DID number
On the Secretary/Admin phone create a Speeddial button that dials 2511 with a Line Text Label called Manager.
When the Secretary/Admin presses the newly created Manager Line Button a direct call will ring 2511/Intercom
line on the Manager phone. It will NOT Auto-Answer and the Manager will either press the Intercom
button to answer the Secretary or ignore the call.
Cheers!
Rob
