Click File, click Status, then click Custom Status.
Click Add.
Type the custom status title, for example, In a Meeting.
Select Busy or Away from the Show As drop-down list. This determines the icon that displays next to your status.
(Optional) Type the text you want to automatically be returned to a user who tries to send you an instant message when you have this status selected, for example, I'm in a meeting right now and can't respond.
Click OK, then click Close.