AASTRA 4420 IP Basic (SIP) for MX-ONE User Guide - Manual (Page 28)

During Calls
Dialog 4420 IP Basic 28
Conference
With this procedure you can include up to seven parties in a
conference. Only the conference leader (i.e. the person initiating the
conference) can admit participants. The conference tone will be
heard every 15 seconds during the conference. The tone is also
heard each time a participant enters or leaves the conference.
Note: The conference tone might be disabled for your
system.
You have an ongoing conversation and want to establish a phone
conference. You will become the conference leader. Ô
Line/Hold Press. z
Call the third party.
Wait for answer. 3
Press
or Ô
Conference press to establish a conference.
Repeat the procedure to add more conference members. d
Replace the handset to leave the conference.
Note: When the conference leader leaves the conference,
the conference will continue with the other included parties.
The conversation is changed back to a normal two party
connection when there are only two parties left.