Aastra M401 User Manual page 38

7.4 BARRING EXTERNAL CALLS FROM YOUR PHONE
You can prevent external calls from being made on your phone.
Locking your extension
On your keypad:
Press the following keys consecutively
You will hear two beeps.
Hang up.
Unlocking your extension
On your keypad:
Press the following keys consecutively
Enter your personal password
You will hear two beeps.
Hang up.
0
0
FOUR DIGITS
5
5
37