They are the "adapter interface" sockets, for the Bluetooth and Ethernet options, just did some digging and I feel 98% sure that is what they are for. There is the 700383771 gigabit ethernet adapter and the 700383789 Bluetooth adapter, these are the only ones I see available at the moment, but presumably they could use the port to add various other devices at some later date. The stand is required when using these add-ons as they mount like warts on the back of the phone.