Rather than logging out, you can lock your phone. You can either lock your phone manually using the steps below or have it automatically locked after a period of phone inactivity. To use the lock feature you need to set a security PIN (you can lock the phone with a code but anyone can also unlock it).
When your phone is locked:
It can only be used to make internal and emergency calls.
None of the menus for your user settings can be accessed.
Unlocking the phone requires your configured login code.
To do this during a call, press the PHONE key and then press Features.