You can set your personal status. Left-click on your Login to open the dialog window.

status image

You can also change your presence status by calling the service number. This number is * 4, by default, but you can change it in the section "Service codes".
Call this number to check your current status or change it by pressing on the corresponding digit.
Default status - onlinestatus image. You can change it to:

status image Away

status image Do not disturb