m4r format not supporting

Question

Thanks in advance,
   We are developing a site specially for mobile in .net. In this we are providing download of ringtones, videos, wallpapers.. But ringtones are not downloaded in  iphone.  Later we came to know that iphone suuport .m4r format. But  m4r ringtones are not downloaded into the iphone( here we are setting content type to application/octate-stream ), it is showing iphone does not support this format.
  I want to know how we should provide download of ringtones to iphone.