1. A computer-implemented method of web service support for a multimodal client processing a multimodal application, the multimodal client providing an execution environment for the multimodal application, the multimodal client operating on a multimodal device supporting multiple modes of user interaction including a voice mode and one or more non-voice modes, the multimodal application stored on an application server, the method including: receiving, by the application server, an application request from the multimodal client, the application request specifying the multimodal application and characteristics for the multimodal device; determining, by a multimodal adapter of the application server, modality requirements for the multimodal application, the modality requirements specifying characteristics of a modality web service capable of processing multimodal applications; selecting, by the multimodal adapter of the application server, a particular modality web service in dependence upon the modality requirements and the characteristics for the multimodal device, including retrieving an interface descriptor for the particular modality web service, the particular modality web service capable of processing portions of the multimodal application that correspond to a particular mode of user interaction; determining, by the multimodal adapter of the application server, whether the multimodal device supports Voice Over Internet Protocol (‘VoIP’) in dependence upon the characteristics for the multimodal device; providing, by the application server, the multimodal application to the multimodal client; and providing, by the multimodal adapter of the application server to the multimodal client in dependence upon whether the multimodal device supports VoIP, access to the particular modality web service for processing the multimodal application.