Dynamically defining a VoiceXML grammar of a multimodal application, implemented with the multimodal application operating on a multimodal device supporting multiple modes of interaction including a voice mode and one or more non-voice modes, the multimodal application operatively coupled to a VoiceXML interpreter, and the method includes loading the X+V page by the multimodal application, from a web server into the multimodal device for execution, the X+V page including one or more VoiceXML grammars in one or more VoiceXML dialogs, including at least one in-line grammar that is declared but undefined; retrieving by the multimodal application a grammar definition for the in-line grammar from the web server without reloading the X+V page; and defining by the multimodal application the in-line grammar with the retrieved grammar definition before executing the VoiceXML dialog containing the in-line grammar.