As machines in most industries continue to grow in complexity, user interfaces play an increasingly important role in allowing operators to naturally interact with such machines. In this paper, we present a versatile approach that can enable operators to interact with a variety of machines using smart mobile devices. A low-cost, embedded system-based setup and an easy-to-implement communication method to wirelessly interface smart mobile devices with physical systems are presented. An application development and evaluation approach is adapted from human-computer interaction research and employed to investigate the functionality and usability of mobile-mediated interactions with physical systems. The approach is applied to the design of a mobile application to interact with a DC servomotor test bed using an ¡Phone.