1. A computer-implemented method of automatically filling a form field in response to a speech utterance in a multimodal communications environment having a Web browser implementing a XHTML+VXML (X+V) markup language, the method comprising: parsing an X+V document to determine a synchronized voice field in a user profile domain, wherein a synchronized voice field refers to a form field that is filled by a synchronization of speech and graphic inputs, and a user profile domain refers to form fields that are to be filled with data corresponding to a user profile; for each determined synchronized voice field, dynamically generating at least one grammar corresponding to the form field at runtime, the at least one grammar being based on a user profile and comprising a semantic interpretation string; and creating an auto-fill event based upon the at least one grammar and responsive to the speech utterance, the auto-fill event causing the filling of the form field with data corresponding to the user profile and comprising at least some data not in the spoken utterance.