As per http://www.emacswiki.org/emacs/IswitchBuffers :
> Note: IswitchB was part of GnuEmacs, but it has been removed starting
> with Emacs 24.4. The Emacs ‘NEWS’ (‘C-h N’) says to use IcompleteMode
> instead, but for those wanting more familiar functionality,
> InteractivelyDoThings is a closer fit.