AASTRA 4420 IP Basic (SIP) for MX-ONE User Guide - Manual (Page 22)

Outgoing Calls
Dialog 4420 IP Basic 22
Press.
Cancel all Callbacks #37#
Dial.
Press.
Activate Call Waiting
If you urgently wish to contact a busy extension or external line, you
can notify by a Call Waiting signal. 5
Press.
or Ô
CallWaiting press.
Note: France and Finland, press
6
; Sweden, press
4
Keep handset off hook. When the called extension or the external
line becomes free, it will be called automatically.
Note: The Call Waiting feature might be blocked for use on
your extension (programmed by your system
administrator). If Call Waiting is not allowed, you will
continue to receive a busy tone.