You can use the lock feature to prevent other people from making external calls from your extension.
This feature uses a 4-digit PIN code which you set when you lock the phone. The same code is required to unlock the phone. If you forget your code that you set, a system phone user can unlock your extension remotely.
2.Dial a four digit code using the 0 to 9 numbers.
3.Redial the four digit code.
2.Dial the four digit code you used to lock the extension.