Calling them is easy as you would do it the usual way with .prompt. Just add 2 Parameters: scope and a configObject (according to the desired widget: comboconfig for promptcombox like you would pass to a combobox, radiogroup config for promptradio and checkboxgroup-config for promptcheckbox.
Find a zip attached with a full working demo file (drop it where ext-all-debug.js resides) and a diff for ext-all-debug.js (3.4.0). As Ext.Messagebox.prompt could not be overriden the usual way you need to modify the library.
i could upload patched versions of ext-all and ext-all-debug , but i am not sure, if that is allowed by sencha