Why can't I import .band files to my iphone via itunes?

I have started file sharing with a friend of mine. He sent me some .band files from projects that he was working on through dropbox. I opened itunes, went to the apps page, went to file sharing, clicked on GarageBand, and tried to drag the files into the file page. It wouldn't let me. I had sent some .band files to my friend and he said they opened without trouble on his computer. Why can't I import his .band files into GarageBand on my iphone?

Any help is appreciated.