A mobile device can include electronic circuitry and a chassis shell adapted to protect the electronic circuitry. The chassis shell includes an opening exposing a tray inside the mobile device. The tray can include an external card slot and a patterned wall. The tray can be disposed within a cavity of a support structure of the mobile device. An input/output (I/O) component, such as a speaker, and a card reader can also be disposed within the cavity. The I/O component can communicate via at least a hole in the patterned wall (e.g., a speaker grill).