Mobile devices are increasingly used for entertainment applications due to their ability to transcend economic and cultural barriers. One promising trend in developing mobile musical application is to simulate mobile devices as various musical instruments, rendering them suitable for real-time music playing and editing. To address some existing challenges, we introduce a novel mobile musical system aiming to simulate the functionality of mu sical instruments and visualize the interaction between simulating devices and mobile users. In practice, we create a friendly user interface on the touch screen of mobile devices to simulate a string or keyboard instrument. The action of finger touch is also visualized on the touch screen in a graphic format. The fusion of music playing and visual responding provides users tactile feedback and better playing experiences. We also optimize the musical algorithm to reduce the audio generation latency by minimizing system computation. The ultimate goal of the mobile musical system is to demonstrate the feasibility and the potential for converting mobile devices into a particular musical instrument. The described system plays an important role in not only serving as a powerful tool for personal entertainment, but also assisting individuals interested in learning and editing electronic music.