I prepared as follows:
There is a page (View) and model (ViewModel) to query the client about methods to be a signature:
void LoadSomeData<t>(object request, Action<response, t> onLoad Action<erroreventargs<t>> onError = null, T userState = null)
The client for service rendered in a separate dll, then everything is as usual, react to user action (via ICommand) pull the appropriate method, at the same time including ProgressIndicator and blocking (if required) interface. Return onLoad or onError, unblocking of the UI and the ViewModel updated the desired fields, say UI it's time to upgrade by implementing the ViewModel from INotifyPropertyChanged.