Laurent Bugnion explains how RelayCommands might work wonders in Silverlight and also in WPF.
In Silverlight, parts of the “plumbing” are available already (the ICommand interface) but most of it is missing. This led some very clever people to implement Commands in Silverlight, to replace the missing pieces by a custom implementation. In Prism, the command implementation is called DelegateCommand. In my MVVM Light Toolkit, I use a command that my good friend, colleague at IdentityMine and fellow WPF Disciple Josh Smith created, called the RelayCommand.