Overhead Paging systems work like a standard 2500 phone. It auto answers the call. Cisco CallManager does not have a dedicated intercom or paging feature. However, you can use the Auto Answer feature in Cisco CallManager. Activating this option or button causes the speaker phone to go off hook automatically when an incoming call is received.

To configure Auto Answer, perform these steps:

On the Cisco CallManager Admin page, go to Device > Phones > Select the Extension. Select Enable the Auto Answer feature.

Choose one of these options to activate the Auto Answer feature for the directory number:

Auto Answer Off

Auto Answer with headset

Auto Answer with speakerphone (intercom)

http://www.cisco.com/en/US/tech/tk652/tk653/technologies_configuration_example09186a008015094e.shtml#conf

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/3_1_1/ccmcfg/b06gtway.html