Kindle page numbers are matched to the page numbers of a paper edition of the book, see
http://www.amazon.com/gp/help/custom...0505500&#pages
Amazon haven't created page numbers for all Kindle books with paper editions yet. If your book isn't available in a paper edition, you'll definitely not get page numbers. If it is available in a paper edition, you may get page numbers at some point in the future.
Calibre works in a different way - it does a "best guess" of page numbers, and generates them accordingly, so it doesn't depend on a paper edition.