Although Graphical User Interfaces (GUIs) often improve usability, individuals with physical disabilities may be unable to use a mouse and keyboard to navigate through a GUI-based application. In such situations, a Vocal User Interface (VUI) may be a viable alternative. Existing vocal tools (e.g., Vocal Joystick) can be integrated into software applications; however, integrating an assistive technology into a legacy application may require tedious and manual adaptation. Furthermore, the challenges are deeper for an application whose GUI changes dynamically (e.g., based on the context of the program) and evolves with each new application release. This paper provides a discussion of challenges observed while mapping a GUI to a VUI. The context of the authors' examples and evaluation are taken from Myna, which is the VUI that is mapped to the Scratch programming environment. Initial user studies on the effectiveness of Myna are also presented in the paper.