AT&T System 25 - Manual (Page 37)

Following
You can have your personal calls sent to another telephone by
using either the Following or the Forwarding feature. To use the
Following feature, at a telephone other than your own, you sign
in your extension number. To cancel the request, you may
either sign out your extension number from that other telephone,
or sign in at your own telephone.
Although Following and Forwarding send your calls to another
telephone, the two features differ slightly. Read the information
and procedures for both features and then. use the one that best
fits your need.
Signing In - At Another Phone
1 Listen for
2 Dial your
3 Dial your
4 Listen for
dial tone, then press
own extension number.
extension number again.
confirmation tone, then hang up.
Signing Out - At Another Phone
1 Listen for dial tone, then press
2 Dial your extension number.
3 Dial .
4 Listen for confirmation tone, then hang up.
Signing Out All Extensions
This procedure signs out all extension numbers that have been
signed in at this telephone except for the one normally assigned
to it.
1 Listen for dial tone, then press
2 Listen for confirmation tone and hang up.