Mobile RFID-enhanced applications ("Mobile RFID") offer a unique way of interacting with the physical world by using the touch paradigm. They offer an intuitive way to interact with physical objects to which RFID transponders are attached. However, the development of mobile RFID applications is not well supported yet, in contrast to stationary RFID applications where typically RFID middleware components are used to integrate RFID technology into information systems. Our ID-Services RFID middleware architecture applies the idea of a dedicated RFID middleware component to mobile information systems and addresses their different requirements with a flexible integration approach based on graduated abstraction and complexity hiding. A major feature of ID-Services is the use of "proxy objects" which allow a transparent interaction with objects from the physical world in the same way as with objects from an object-oriented programming paradigm. We propose a design and development methodology for the use of ID-Services that helps speeding up the development process of mobile RFID applications and keeps both design and implementation phases simple, by fully externalizing the complex, RFID-specific concepts and technical details to the ID-Services middleware.