a finger gesture user interface for an electronic device , including a housing for an electronic device including a front opening in a front outer surface of the housing , a rear opening in a rear outer surface of the housing , and inner sidewalls extending from the front opening to the rear opening to form a cavity , a display , mounted in the housing along a plane transverse to the front and rear openings , for rendering a 3d realm , a detector mounted in the inner sidewalls , operable to detect translation of a finger inserted in the cavity along a dimension of the cavity transverse to the display plane , and a processor connected to the detector and to the display for interpreting the detected finger translation as a user interface input command to move within the 3d realm along the dimension transverse to the display .