You don't need calibre to read an HTML book. Use whatever browser you fancy, IE, Firefox, Safari, Opera by choosing File, Open File.
Calibre is made primarily for organizing and converting between different formats. It has a viewer so you can see how your conversion is doing, rather than for reading.
I don't have an iphone, so I don't know what program is used for that if you are wanting to view the book on your iphone.
Last edited by mrmikel; 05-04-2010 at 10:28 AM.