AT&T System 25 - Manual (Page 58)

Following (Continued)
Signing Out All Extensions
This procedure signs out all extension numbers that have been
signed in at this telephone except for the extension normally
assigned to it.
1 Listen for dial tone, then press
❑❑❑
* *
0
.
2 Listen for confirmation tone and hang up.
Display
The characters dialed (including * *) appear on the display
screen.
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