A single dual-modality client application both group messaging and group board modalities for a selected user group. Both group messaging and group board data content is transmitted and received in group data objects. Each group data object comprises an indicator of modality denoting one of the two modalities. Separate group messaging and group board display interfaces are provided by the client application for the selected user group. Group messaging display data for displaying at least part of the content of the group messaging modality data objects associated with the currently selected group as a sequence of messages on the group messaging display interface, and group board display data for displaying at least part of the content of the group board modality data objects associated with the currently selected group as a collection of posted items on the group board display interface are generated by the client application.