Devices and systems are disclosed which relate to enabling NFC communication on devices such as an iPhone. A traditional smart card tray is modified to include contact leads from the inside of the smart card tray to an exterior surface of the smart card tray. Exposed contacts on the external surface provide an outside interface for add-ons. An exemplary add-on is an NFC circuit coupled to or embedded within a mobile device skin. The skin fits snugly around a portion of the mobile device, and includes on one surface contact points that line up with the outside interface of the mobile device. The contact points provide electrical communication between NFC circuitry of the mobile device skin and the smart card within the mobile device. When the skin is worn on the mobile device, the mobile device is NFC enabled. When the skin is removed, the NFC is no longer available.