Mobile user interfaces are some of the most convoluted pieces of work. You need to plan out specific functions and manage how users will interact with these different screen elements. One such example is knobs found on electronic equipment. Many music-based mobile apps utilize this piece of UI for many different reasons. And there are plenty of examples on Dribbble which express enormous bouts of creativity.
In my gallery below I have put together a great deal of knobs and button interfaces. These are mostly from mobile web apps, but also feature illustration work. Ultimately any designer can figure out how to build such a unique mobile setup. However programming the interface to work in Android or iOS is another topic. I hope these ideas can provide inspiration to move through that first step of design mockups.