Due to obvious portability constraints, mobile technology excludes large electronic displays for visual immersion. On the contrary, sound heard over headphones is ideally suited for mobile applications. The use of stereo headphones or stereo speakers on mobile devices enables to take advantage of binaural technology which can provide an immersive sound experience for a variety of applications ranging from stereo widening of music (creating an out of the head listening experience) to full 3-D positional audio. Advances in audio are going to help bring in richer multimedia, increase quality of mobile music and help create more interactive and immersive audio applications. Interaction with sound in 3D audio space is no more limited to indoor environment [8]. In this paper, we report on an architecture for multimedia applications on mobile devices separating content creation (audio and graphics) from content manipulation. We have developed a markup format for interactive and spatialized audio on mobiles which can be used an interface between the sound designer and the application programmer. After presenting an overview of the key concepts in designing a format for interactive and spatialized audio and the methodology used to build the corresponding sound API , we describe its use in a mobile immersive music application for Copenhagen Channels where interactivity with the music is done through GPS waypoints.