From what I've heard/read, the Mormon religion has several similarities to Christianity. They believe in what the Bible teaches, but only follow the King James version as it supposedly "less corrupt." As far as Heaven and Hell, they believe in something called "3 levels of glory." If you want to find more information on the religion you can look here: http://www.utlm.org/faqs/faqgeneral.htm#5
They might call themselves Christians because of the basis that their religion is founded upon? Mormons do however, have a religion that most people would consider seperate from Christianity.