Handset Lock
You can lock the handset to prevent unintentional button presses.
To lock the handset:
1.Press the Options/Mute button.
2.Press the SHOW softkey. The display shows "1. Ring Type".
3.Press the NEXT softkey until the display shows "3. Lock Handset".
4.Press the OK softkey. The display shows "Handset Locked".
To unlock the handset
zPress 
then *.
Handset Asleep Mode
If your phone remains idle for more than 15 seconds, it automatically reverts to Handset Asleep mode. To wake up your handset, press any key.
Call indications: While your phone is asleep, it does not display message waiting indicators or indications that the
Priority calls with Do Not Disturb active: When the phone is asleep and a priority call is made to the phone, it appears to the caller that the priority call was successfully connected, even though you receive no indication on your phone. To ensure that your phone provides proper audible and visual ring notification when Do Not Disturb is on, always press the line/intercom button and the 
button when the phone wakes up.
Headset Calls
Phone functions and features are the same when a headset is plugged into the headset port of the phone (on top of phone, above the volume button).