Precondition: You must have configured a personal identification number (PIN) for your telephone . 

To lock and unlock the telephone:

Lift the handset.  

Enter the code for "off" or "on". 

Enter the telephone lock PIN . 

While the telephone is locked, a special dial tone sounds when you lift the handset. You can continue to dial internal numbers as usual.  An authorized party can also lock and unlock your telephone.