This paper describes a set of phone classification experiments based on electromyography (EMG) signals and a subsequent phone confusion analysis, as part of a project that aims to restore speech for Spanish laryngectomees by developing a Silent Speech Interface (SSI). Understanding the relationship between speech and the muscles used for speaking is essential to learn the possibilities and limitations of such EMG-based SSIs, before advancing to a complex task such as direct EMG-to-speech conversion. When considering only information from the muscles of the face and neck, important information from the tongue and vocal cords is missing. This is reflected in the results, which show confusion between pairs of phones that only differ in the position of the tongue or the voicing feature.