AT&T 7406BIS - Manual (Page 45)

Priority Calling
To place a priority call 1 Press [
Priority
] (while off-hook)
(3-burst ring) or dial Priority Calling code (while off-hook)
[dial tone]
2 Dial extension
To change a regular 1
call into a priority call
(3-burst ring) when you
hear a call-waiting
ringback tone
2
Press [ Priority ]
●
Called party receives a priority call-waiting tone
(3-burst ring)
Wait for called party to answer
Note: If you still receive a call-waiting ringback tone,
wait a few minutes and try again.