In a network environment, no matter if Internet or personal area network, many devices, applications, and services, which can be added and removed dynamically, are accessible by the user. An intelligent human interface to such an environment needs to adapt to changes in the network. This does not only concern input, output or understanding parts bnt also the knowledge about functionalities provided by the network. In this paper we describe, how to enhance a multi-modal dialogue system with a planning module, consisting of a reasoning component and abstract models describing the functionalities of the devices, applications, and services which are part of the network. This additional component allows to support plug&play and to serve complex user wishes according to the current available functionalities in the network. The work described in this paper was snccessfully integrated in the prototype system SmartKom.