The first part of connection is fine, after we press conf key for the first time the person that was connected initially hears music, after this caller dials number to third party, they can hear each other and presses conf button again, after this (here is an update from customer) callers connect to PBX, and hear prompt from it(the connection is not dropped as said in the initial post).
How can we force phones to use internal conference bridge? I suppose that problem may somehow be related to PBX taking part in conference.
Configure Multicast Paging on the Cisco IP Phone 7800 Series or 8800 Series Multiplatform Phone
The Cisco IP Phone 7800 and 8800 Series Multiplatform Phones provide voice communication over an Internet Protocol (IP) network...
Add Call Park on a Cisco 7800 or 8800 Series Multiplatform Phone Key Expansion Module
Call park allows the user of the phone to put an incoming call on hold so that the call can be retrieved on another phone. A call is park...