The attached two page PDF describes what an Eclipse virtual party-line (conference) is and how to setup it up in Eclipse software. 
A virtual party-line (conference) is like a standard telephone conference. When person A speaks—everyone hears them, when person B speaks everyone hears them. To participate in a party line a user with a Station needs a key programmed to talk or listen to the Party Line (Conference).
Interfaces can also be assigned as members to a party line but these will be permanently in it.  ECS 5.2 maximum # of configurable party-lines is 198 (maximum 99 members in each)
Create a new party-line by pressing the “NEW” button and give it a specific name.  Attach any permanent members to the party-line by moving them from the  available section to the attached section .
Note:  Do not  place  panels in the  attached section, instead add the  party-line  keys to the  user panels by giving them talk and listen keys
Customize the  party-line by selecting options in the “Properties “ screen on the  right hand  window .  Repeat the previous steps for creating additional party-lines
Note:  The available and attached work screens have tabs that allow the user to look for specific  label types (all, interfaces and panels)