You might want to check out this thread:
https://www.mobileread.com/forums/sho...+iphone&page=4
I have been reading Non Amazon books for months across Kindle 3, iPad2 and iPhone 4 thanks to the very generous folks here on MobileRead.
I am not emailing the books to my Kindle apps on the iPad or iPhone, instead placing the books in a very specific location that allows for syncing.