You can assign any telephone to an intercom group. However, only multi appearance telephones can make and receive intercom calls. Single-line telephones can only receive intercom calls. Multiappearance telephones must have at least one open or available call appearance to receive intercom calls.

An intercom call makes a unique alerting sound. If the telephone has an intercom button with a status lamp, the lamp also flashes.

You can establish an automatic intercom call between two telephones, even if the Class of Restriction (COR) does not support other calls between them.