Hi Satu,
Just to add a note to the great tips from Pam and James (+5 points each folks :)
Don't feel stupid my friend, there are so many acronyms in this business it will make your head spin :)
ACD = Automatic Call Distribution (calls are distributed between active/logged-in Agents)
This term relates to Call centre applications like UCCX.
As to Hunt Group Login/Logout, sadly this feature is only available CCM 4.2 and CUCM 6.x/7.x with the Login/Logout of Hunt Groups feature (as James nicely noted). This is not available in CCM 4.1.3 or 5.x. Have a look;
Log Out of Hunt Groups
The Log Out of Hunt Groups feature allows phone users to log their phones out from receiving calls that get routed to directory numbers that belong to line groups to which the phone lines are associated. Regardless of the phone status, the phone rings normally for incoming calls that are not calls to the line group(s) that are associated with the phone. The phone provides a visual status of the login state, so the user can determine by looking at the phone whether they are logged in to their line group(s).
The Log Out of Hunt Groups feature also comprises the following components:
The HLog softkey allows a phone user to log a phone out of all line groups to which the phone directory numbers belong. Configure the HLog softkey in the Softkey Layout Configuration window. When the user presses the HLog softkey, the phone screen displays "Logged out of Hunt Group." When the user presses the HLog softkey again to log back in and receive hunt group calls, the "Logged out of Hunt Group" notification on the phone screen clears.
The Hunt Group Logoff Notification service parameter in the Clusterwide Parameters (Device - Phone) section of the Service Parameters Configuration window for the Cisco CallManager service must be configured to enable this feature.
Hunt Group Logoff Notification Service Parameter
The Hunt Group Logoff Notification service parameter in the Clusterwide Parameters (Device - Phone) section of the Service Parameters Configuration window for the Cisco CallManager service provides the option to turn audible ring tones on or off when calls that come in to a line group arrive at the phone and the current status of the phone is logoff. The default value specifies None, which causes the phone not to ring.
The Log Out of Hunt Groups feature, which is device-based, operates differently for non-shared lines and for shared lines.
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/4_2_1/ccmsys/a03rp.html#wp1091630
In the CCM 4.1.x and 5.x trains there is really not an equivilant feature. The best you can do is probably using AC Hunt :(
Hope this helps a little!
Rob
