This easy-to-follow video tutorial from CNET explains how to create iPhone ringtones using just the iTunes software – the steps stay the same for both Mac and Windows computers.
You may use iTunes to convert any MP3 song into an iPhone ringtone provided the song file is not protected by DRM. This means the technique won’t work with iTunes store music but is perfect for creating ringtones from songs that you purchased from Amazon store or ripped from a CD.