The fundamental problem here is that "Christian" admits different meanings. In a broad sense, a Christian is anyone who self-identifies as a follower of Jesus Christ (cf. [Acts 11:26][1]), which would include all bodies such as Catholics, Orthodox, Anglicans, Protestants, and Restorationists (including JWs and Mormons). 

To use "Christian" in a narrower sense, one would need to choose some criterion of orthodoxy by which to judge groups. One common standard are the ecumenical creeds, which JWs and Mormons reject.
	
In a [debate][2] from a few years back, evangelical Albert Mohler and Mormon Orson Scott Card went back and forth about whether Mormons are Christians. (The debate is hard to navigate, but it's all there; use the "previous" button at the bottom to get back to the beginning). Mohler argues, in short, that Mormons don't hold to the ecumenical creeds about the nature of God and Christ, which the wide majority of Christians share, and Card responds by saying that Mormons are "non-traditional Christians," or followers of Christ who reject the tradition embodied in the creeds.


  [1]: http://www.biblegateway.com/passage/?search=Acts11.26
  [2]: http://www.beliefnet.com/columnists/blogalogue/are-mormons-christian/