AT&T 7406BIS - Manual (Page 28)

Note: You can privately discuss call; if coworker is not
available, press the fluttering [ xxxxx ] to reconnect to call.
If your coworker has activated Send All Calls, you must
use [
Consult ] to reach your coworker.
3
[ Conference ] to make it a 3-party call
Press [ Transfer ] again to send call to coworker or press